Early luteal concentrations of progesterone were a reasonable predictor of concentrations on day seven and could be used to predict animals at risk of embryo loss.

Just one of the interesting findings of a trial, carried out by scientists in Ireland, to establish the relationships between plasma concentrations of progesterone (P4) during the early luteal phase and subsequent embryo survival rate.

“We also wanted to find out more about the repeatability of P4 concentrations during the early luteal phase from cycle to cycle in dairy heifers,” explained Teagasc’s Mervyn Parr, speaking at this year’s British Society of Animal Science’s annual conference, held at Queen’s University, Belfast.

In cattle, early embryo death is a major cause of cow reproductive wastage. Low post ovulatory systemic progesterone (P4) or a delay in the normal increase in P4 concentrations during the early luteal phase have been associated with reduced embryo survival rate in dairy cows.

So, to find out more, the team synchronised oestrus in 118 Holstein-Friesian heifers using two injections of a synthetic prostaglandin administered intramuscularly 11 days apart.

At the oestrus following the second injection, heifers were artificially inseminated (AI) by one of two operators using thawed frozen semen from one high fertility bull. Embryo survival was determined by ultrasonography on day 30-35 after AI.

A positive pregnancy diagnosis was based on the presence of an apparently viable foetus with a visible heartbeat and clear amniotic fluid. Following pregnancy diagnosis all heifers were injected with synthetic prostaglandin to induce embryo loss and return to oestrous cycles.

Six weeks after the induced embryo loss, the entire experimental protocol was repeated on all heifers. All inseminated heifers were blood sampled twice daily (am and pm) on days four, five, six and seven following each insemination.

Concentrations of P4 were determined by radioimmunoassay and a mean concentration of P4 was calculated for each day.

“And we found that there was both a linear and quadratic relationship between concentrations of P4 on days four to seven and changes in P4 between these days and embryo survival rate,” said Mr Parr.

“Increasing concentrations of P4 were associated with increasing embryo survival rates although embryo survival declined at very high concentrations of P4. Early luteal phase concentrations of P4 had a low repeatability from cycle to cycle,” he added.

Presented to the British Society of Animal Science Annual Conference, 12-14 April, 2010, Queen’s University, Belfast.

Parr MH, Mullen MP, Crowe MA, Roche JF, Lonergan P, Evans ACO and Diskin MG: “The relationship between plasma progesterone concentration during the early luteal phase and embryo survival in dairy heifers.”

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Recent trials have revealed that fertilisation failure occurred in 53.5% of dairy animals (67.5% of cows, 18.8% of heifers) – a figure that is greater than previous estimates of between 10 and 20%. And the work also revealed that energy status in early lactation significantly affected fertilisation rate.

The cost of replacing cows that are culled due to reproductive failure is approximately £18,000 per 100-cow herd per year. It is estimated that fertilisation rates following artificial insemination are >90% and yet calving rate to a single insemination is in the order of 31%.

“The majority of this reproductive wastage occurs between insemination and maternal recognition of pregnancy, approximately 16 days after ovulation, with relatively
little late embryonic/foetal mortality,” the Agri-Food and Bioscience Institute’s Ryan Law told to delegates at this year’s British Society of Animal Science’s annual conference, held at Queen’s University, Belfast. 

The objective of his team’s study was to quantify reproductive wastage prior to day seven post insemination and to evaluate energetic, metabolic and hormonal effects in early lactation (day 0-42) on embryonic loss.

The first study involved 63 autumn-calving Holstein Friesian cows and 32 Holstein Friesian heifers. Lactating cows were offered a total mixed ration (TMR) comprising 60% concentrates and 40% forages (60% grass silage and 40% maize silage) on a DM basis. The complete diet contained 185 g CP/kg DM and 12.4 MJ ME/kg DM. An average daily energy balance for each individual cow was calculated for each week of lactation. Heifers were offered ad-lib grass silage and 3kg of concentrate per head per day.

A second study was conducted on 16 spring calving Holstein Friesian cows and 18 heifers to validate the technical aspects of single embryo recovery. Lactating cows were offered a TMR comprising 50% concentrate and 50% forage (65% grass silage and 35% maize silage) on a DM basis. Heifers were offered ad-lib grass silage and 3kg of concentrate per head per day. Individual cow intakes were not recorded in Study 2.

Oestrous cycles were synchronised to ovulate at days 42, 70 and 98 post calving in the first study and 61 days post-calving in the second study, using a controlled intra-vaginal drug release (CIDR) of progesterone.

Animals were bred by AI approximately 56 hours after CIDR removal. The uteri of all animals were nonsurgically flushed seven days post-insemination to recover and classify embryos; the proportion of unfertilised oocytes, degenerate embryos and viable embryos (morula/blastocyst stage) was recorded.

“And we found that the recovery rate did not differ between heifers and cows,” said Dr Ryan. “But the proportion of oocytes fertilised (as a proportion of recovered structures) was significantly lower in lactating cows than heifers – 32.5% compared to 81.3% respectively.

“Reproductive wastage during the seven-day period post insemination was lower than anticipated, with 15.4% of fertilised oocytes from lactating cows being degenerate,” he added.
Presented to the British Society of Animal Science Annual Conference, April 12 to 14, 2010, Queen’s University, Belfast.

Law RA, Williams EJ, Gilmore HS, Carter F, Young FJ, Lonergan P, Crowe MA, Diskin MG, Ferris CP and Evans A: “Incidence of fertilisation failure and embryo loss in Holstein Friesian heifers and post-partum dairy cows.”

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There is a detrimental effect of a bad calving on cows’ subsequent fertility and milk production. When calving difficulty increases, fertility declines and milk yield in the first stage of lactation also decreases.

Some of the key findings of a recent trial, carried out by scientists in Scotland, which were presented to delegates at this year’s British Society of Animal Science’s annual conference, held at Queen’s University, Belfast.

Being one of the most economically significant non-production traits, calving ease has a large impact on the dairy industry. “And, in addition, calving difficulty is ranked an extremely painful condition of cattle, which suggests that the impact of this trait also greatly affects animal welfare,” said the Scottish Agricultural College’s Sophie Eaglen.

“It is therefore plausible that there will be a detrimental effect of a difficult calving on the subsequent performance of the animals involved. So the objective of our study was to use UK Holstein-Friesian cattle data to phenotypically analyse the effect of calving ease on fertility and milk production, of both cow and calf, in their subsequent lactation,” she added, explaining the rationale behind her team’s work.

Using first parity calving ease records only, provided by the Cattle Information Service (CIS) and National Milk Records (NMR), the team merged the calving ease and fertility data to produce a total of 32,483 and 8,184 records of cow and calf, respectively,  originating from 2,486 and 1,410 herds.

Fertility data consisted of the calving interval (CI), number of inseminations (NINS), non-return at 56 days (NR) and days to first service (DFS), of the first lactation following the recorded calving.

Merged calving ease data and production data led to a total of 348,648 and 81,885 records of cow and calf, originating from 2,148 and 1,153 herds, respectively.

“And we found that there was a significant difference in the fertility of cows for different categories of calving ease. Between an easy calving (1) and vet assisted calving (4), there was an increase of 28 days in CI, 0.7 services in NINS, and seven days in DFS,” said Miss Eaglen.

NR showed a decrease of 9% between an easy and vet assisted calving, though this was not significant.

The effect of calving ease on the cumulative milk yield of the first three test days showed a significant difference between all calving ease categories in the cow analysis. Between an easy and vet assisted calving, milk yield decreased by, on average, 1.67kg per test day or 6.1%.

“A significant effect of calving ease on the subsequent production and fertility of the calves was not found. Though, calves which were delivered with veterinary
assistance showed a tendency to decrease in milk yield in the first stage of their lactation as heifers, in comparison to calves delivered with moderate farmer assistance,” said Miss Eaglen, adding that further study is needed to analyse the effect of calving ease on the full subsequent lactation.

Presented to the British Society of Animal Science Annual Conference, 12-14 April , 2010, Queen’s University, Belfast.
Eaglen SAE, Woolliams JA, Coffey MP and Wall E: “Effect of calving ease on the subsequent performance of cow and calf in UK Holstein Friesian cattle.”

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It is not genetic merit for milk production or breed that has an adverse impact on embryo quality, but rather that a variety of factors associated with milk production, such as metabolism and nutritional management, induce hostile conditions that prevent optimal embryo development.

So says Belgium’s Jo Leroy, who led a study to examine the consequences of metabolic changes in high-yielding dairy cows on oocyte and embryo quality.

“Unsatisfactory reproductive performance in dairy cows, such as reduced conception rates, in addition to an increased incidence of early embryonic mortality, is reported worldwide and has been associated with a period of negative energy balance (NEB) early post partum,” he said.

Typically, NEB is associated with biochemical changes such as high non-esterified fatty acid (NEFA), high β-hydroxybutyrate (β-OHB) and low glucose concentrations. So his team’s work looked at and analysed the concentrations of these and other metabolites in the follicular fluid (FF) of high-yielding dairy cows during NEB.

These were then replicated in in-vitro maturation models to investigate their effect on oocyte quality.

“And the typical biochemical serum changes observed in dairy cattle during the negative energy balance early post calving are well reflected in the FF of the dominant follicle, thus exposing the granulosa cells and the maturing oocyte,” he said.

In vitro maturation models revealed that NEB was associated with elevated NEFA and lowered glucose concentrations are indeed toxic to the oocyte, resulting in both diminished oocyte maturation and embryo developmental competence.

Even after the period of NEB, and when the carry-over effects of the NEB were no longer present, high-yielding dairy cows produced statistically significantly inferior embryos in comparison with dairy heifers and beef cows.

“With a newly developed lipid evaluation technique, it was possible to demonstrate that high-producing dairy cow embryos contained up to 45% more lipids, compared to the embryos of non-lactating animals,” added Professor Leroy

“Further research is required to fully comprehend how a dairy cow’s milk production and nutrition influences embryo health and metabolism via an altered environment in the oviduct and uterus.”

Full Paper.pdf

Full details: Leroy JLMR, Van Soom A, Opsomer G and Bols PEJ: “The consequences of metabolic changes in high yielding dairy cows on oocyte and embryo quality.” Animal  2, 1120-1127 www.bsas.org.uk     For further information contact: BSAS on 0131 4 45 4508

Dairy cow fertility is negatively associated with both genetic merit and level of production, and various other factors including season of calving, lactation number and difficult calvings.

“Level of production had a larger effect on fertility performance than genetic merit for milk production suggesting that infertility at an individual cow level is more likely to be associated with increased production and an inability to meet the nutritional requirements of the cow,” said the Hillsborough-based Agri-Food and Bioscience Institute’s David Mackey.

He and his team examined the relationships between genetic merit for milk production and animal parameters and various parameters of reproductive performance using multi-level binary response analysis in a study of 19 dairy herds for three successive years, representing approximately 2,500 cows per year.

The proportion of cows intended for rebreeding that were back in-calf again within 100 days of calving and the proportion of cows that reappeared again with 365 and 400 days of a previous calving were considered in addition to the traditional measures of reproductive performance.

“And we found that level of production has the greatest negative effect, particularly when considered over a 305-day lactation, indicating that infertility at an individual cow level in this study is predominantly due to an inability to meet the nutritional requirements of high genetic merit dairy cows, as evidenced by lower nadir milk protein concentrations.

“These results also suggest that it is possible to achieve good reproductive performance from high genetic merit dairy cows providing high levels of fertility management and appropriate nutrition are achieved,” added Dr Mackey.

 Full Paper.pdf     

Full details: Mackey DR, Gordon AW, McCoy MA, Verner M and Mayne CS: “Associations between genetic merit for milk production and animal parameters and the fertility performance of dairy cows.” ANIMAL 1, 29-43   www.bsas.org.uk

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Selection of the best dairy animals for breeding could be made on the basis of juvenile predictors through the use of genotyping coupled with phenotypic profiling of type traits and metabolic parameters.

Just one of the conclusions of a study, carried out by UK scientists, to determine factors influencing heifer survival and fertility on commercial dairy farms.

The average dairy cow survives only three lactations, reducing the availability of replacement heifers. Prenatal losses occur due to early embryonic mortality, later embryo loss or abortion.

A recent survey of 19 UK herds showed that 7.9% of calves were born dead and 3.4% died within a month. During the rearing phase, 6.7% of animals were lost before reaching first service at 15 months due to disease or accident and another 2.3% failed to conceive.

“Many potential replacements therefore never enter the milking herd. This severely limits opportunities for on-farm selection of breeding cows in addition to presenting a welfare issue and causing economic loss,” said Claire Wathes, from the Royal Veterinary College, explaining the rationale behind her team’s work.

“We have investigated some possible juvenile predictors of future performance. Low-birth-weight calves were more likely to come from either primiparous mothers or older dams with higher peak milk yields, suggesting that the uterine environment may limit prenatal calf growth due to competition for nutrients with maternal growth or milk production.”

The team also found that linear trait classification scores for frame size show genetic correlations with longevity. The skeletal measures of height and crown rump length in one-month-old calves was correlated to subsequent stature, and frame size was correlated to weight at 15 months.

“It may, therefore, be possible to predict performance from simple size measurements as juveniles,” said Professor Wathes.

She added that high lifetime milk production is achieved by a combination of reasonable yields with good fertility and longevity. “Single nucleotide polymorphisms (SNPs) are being identified, which have marked effects on milk production and will almost certainly also affect longevity.

“Size and growth rate measurements made from birth until first breeding at 15 months of age predict aspects of both fertility and milk production. And our results suggest that cows with a high potential to partition energy into milk in early lactation may suffer reduced longevity and that it may be possible to predict this at six months of age.”

 Full paper.pdf        

Full details: Wathes DC, Brickell JS, Bourne NE, Swali A and Cheng Z: “Factors influencing heifer survival and fertility on commercial dairy farms.”   Animal 2, 1135-1143      
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Suffolk lambs grow faster than Texel lambs when parasite infection is minimised.  And the interaction between breed and level of parasite challenge shows that the breed differences in lamb growth depend on level of parasite challenge. 

Just two of the findings of research, carried out by scientists at Teagasc in Ireland, to evaluate differences in breed performance when grazed under contrasting level of parasite challenge.

“We also found that the impact of parasite infection on Suffolk lambs increases as the grazing season progresses,” Seamus Hanrahan told delegates at this year’s British Society of Animal Science’s annual conference, held at Queen’s University, Belfast.

Suffolk sheep have substantially lower faecal egg counts for gastrointestinal nematode parasites than co-grazed Texel sheep and these breeds also have different nematode burdens in the abomasum and small intestine.

The impact of these differences in resistance to parasite infection on animal performance needs to be established in order to determine whether there are breed differences in resilience to gastrointestinal parasite infection,” said Dr Hanrahan, explaining the rationale behind his work.

The study was repeated over two grazing seasons using 143 Suffolk and 151 Texel lambs from the Teagasc flock. The ewes in these flocks are housed between December and lambing (early to mid March) and are turned out, with their lambs, to pasture within two to three days after lambing.
Lambs were weighed at 18 weeks of age and the level of nematode infection was monitored by faecal egg counts at regular intervals up to 18 weeks of age and the number of infective larvae on pastures was evaluated weekly in year one.

Two pastures with different grazing histories were used. The ‘clean’ pasture’s sward was established in the autumn prior to year one of this study and not grazed by sheep prior to turnout in spring of year one. And the ‘dirty’ permanent old pasture that had been grazed by sheep only for at least 10 years prior to year one.

The management of the ‘clean’ sward during the late summer and autumn of year one was designed to minimise any accumulation of infective larvae so that herbage larval challenge in year two was maintained at a low level.

“We found that the ‘clean’ group had essentially zero counts at 14 weeks whereas the dirty group averaged 300 eggs/g,” said Dr Hanrahan.

There was a highly significant breed and pasture type interaction for weights at 14 and 18 weeks of age and growth rate from five weeks to weaning.  “These interactions reflected the much greater impact of ‘dirty’ grazing on Suffolk lambs,” explained Dr Hanrahan. “At 18 weeks of age Suffolk lambs on ‘dirty’ pasture were 4.6kg lighter than Suffolk lambs on ‘clean’ pasture whereas the corresponding difference for Texel lambs was only 1kg.” 

There was no evidence for an effect of grazing treatment on lamb growth rate between birth and five weeks and it was evident that the negative impact of dirty grazing on Suffolk lambs increased as the season progressed. 

“There was also evidence for a breed x grazing treatment interaction for some aspects of ewe performance,” added Dr Hanrahan. “The live weight of Texel ewes at weaning was unaffected by grazing system whereas Suffolk ewes on the ‘dirty’ pasture were 4.7kg lighter than those on ‘clean’ pasture.”

Presented to the British Society of Animal Science Annual Conference, 12-14 April , 2010, Queen’s University, Belfast.

Full details: Hanrahan JP and Good B: “Performance of Suffolk and Texel sheep grazing pastures that presented contrasting levels of parasite challenge.”

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Grazing lambs on chicory produces heavier carcases with a better killing out percentage. Female lambs also demonstrated increased loin juiciness. These were just two of the findings of a trial, carried out by UK scientists, which were presented to delegates at this year’s British Society of Animal Science’s annual conference, held at Queen’s University, Belfast.

A growing body of evidence shows that lambs grazing pure stands chicory grow faster, finish earlier in the season, and have lower levels of parasitism. “However, it is not known if chicory affects meat eating quality, although carcasses may be leaner when market weights are reached, compared to a more slowly finishing on grass/clover mixtures,” said the Scottish Agricultural College’s Jos Houdijk, who led the trial.

“Dietary influences on meat quality should be considered as these are very relevant for consumer acceptance. So we set out to assess the effect of chicory grazing on killing out percentage and meat eating quality in lambs.”

Lambs grazed pure stands of chicory (CH) or grass/clover (GC) from turn-out at 32 days of age for 20 weeks. Body weight was taken just before slaughter. Carcasses were hip-suspended at 2°C for 24 hours before posterior 20cm of left loins were retrieved, matured at 2°C for another nine days in vacuum bags and frozen pending sensory quality assessment at the University of Bristol.

Loins were thawed overnight, de-boned on the day of assessment, cut in 8-10 2-cm thick samples and cooked until internal temperature reached 75°C. Samples were placed in an incubator (60 ºC) prior to sampling by 10 qualified assessors, who were asked to rate it on eight-point category scales for tenderness, juiciness, lamb flavour intensity, abnormal lamb flavour intensity and two hedonic scales for flavour liking and overall liking.

“And we found that chicory grazed and grass and clover grazed lambs weighed 39.1kg and 36.4kg respectively. Killing out percentages were 39.9% and 37.2% respectively,” said Dr Houdijk.

His team also found that female chicory-grazed lambs had juicier loins than grass-and-clover grazed lambs with reduced grassy flavour. However, in some sub-panels, effects on juiciness were stronger and CH loins were scored as being tenderer than GC loins, with a higher livery flavour.

“Beneficial sensory scores for eating quality were given to chicory-reared lamb in several sub-sets, but these were cancelled out when data was pooled, suggesting the need for relatively large numbers of observations to avoid drawing invalid conclusions,” stressed Dr Houdijk.

“Although it can not be excluded that sex-specific effects observed in this study would not be present had lambs been finished to commercial standards, overall the data suggest that using chicory as an alternative crop for finishing lambs is expected to yield higher carcass weights without detrimental effects on meat eating quality,” he added.
             
Presented to the British Society of Animal Science Annual Conference, 12-14 April, 2010, Queen’s University, Belfast.

summary.pdf       presentation.pdf

Houdijk JGM, Nute GR, Navajas EA, Richardson RI and Ross DW: “Effect of chicory grazing on killing out percentage and meat eating quality in lambs.”

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High quality maize silage is an ideal forage for finishing lambs indoors, achieving higher intake characteristics and increasing daily live weight gain by up to 50g/d compared to lambs offered medium-quality grass silage.

“However the benefits in lamb performance decrease significantly when diets contain high levels of concentrates,” the Hillsborough-based Agri-Food and Biosciences Institute’s Ronald Annett told delegates at this year’s British Society of Animal Science’s annual conference, held at Queen’s University, Belfast.

Within sheep systems in the UK and Ireland it is common for hill lambs to be housed late in the season and finished on high grain diets due to inadequate supplies of grass. “However, due to a number of factors, concentrate feed costs have increased significantly in recent years so there is a need to investigate lower cost alternatives,” said Dr Annett, explaining the rationale behind his team’s work.

Forage maize has increased in popularity over the past 10 years and offers some opportunities to reduce forage costs on mixed beef/sheep farms, with the potential for high dry matter yields of high quality material from a single harvest.
 
“But there is limited information on supplementation strategies for lambs offered maize silage. So we set out to investigate the performance and carcass characteristics of lambs finished on grass silage or maize silage at two contrasting levels of concentrates,” he added.

 Sixty crossbred lambs of mixed breeds, with a mean age of 217 days and a mean live weight of 35kg, were allocated to four groups. Lambs were housed in groups of six and offered ad-lib grass silage (G) or maize silage (M) plus concentrates. Concentrates were offered to achieve a high or low proportion of forage in the diet, giving a total of four treatments.

Intake of silage and supplement were recorded daily. Lambs were weighed fortnightly until they reached their target slaughter weight of 44kg. Cold carcass weight, dressing proportion and grade were recorded at the point of slaughter.
Carcass conformation and carcass fatness were also both scored.

“Intake of maize silage was 17% higher than grass silage for lambs on the high forage diet, and 14% higher on the low forage diet,” said Dr Annett. “And total DM intake increased by 15% when lambs were offered maize silage rather than grass silage. Consequently, daily live weight gain was 34g/d higher for maize silage-fed lambs.”
 
Reducing the forage proportion from 0.80 to 0.50 decreased the intake of grass silage and maize silage by 17% and 14% respectively, but increased total DM intake by 32% and average daily live weight gain by 53g/d.

“Finishing diet had no effect on carcass fatness, but with grass silage-fed lambs only, carcass conformation increased and dressing proportion tended to increase as the proportion of forage in the diet increased,” he added.

Presented to the British Society of Animal Science Annual Conference, 12-14 April, 2010, Queen’s University, Belfast.

Annett RW and Carson AF: “Effects of silage type and proportion in the diet on the growth and carcass characteristics of finishing lambs.”

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Dietary vitamin E level did not affect lamb performance, but those fed grass silage grew more slowly and had a higher feed conversion ratio than those fed concentrates. Just some of the findings of a trail, carried out by UK scientists, in order to determine the effect of dietary vitamin E level and basal diet on vitamin E status, performance and tissue fatty acid content in lambs.

“Vitamin E deficiency is associated with white muscle disease in lambs, but low levels can also reduce the shelf life of the meat” said the University of Bristol’s Eleni Kasapidou, explaining the rationale behind her work. Five groups of eight Suffolk cross Charolais wether lambs, with an initial live weight of 28.4kg, were allocated to one of five concentrate-based diets supplemented with all-rac α -tocopheryl acetate to contain 30mg, 60 mg, 120mg, 250mg, or 500mg of α-tocopheryl acetate per kilogram of dry matter for 63 days.

Two additional groups of eight lambs entered the study at 31.2kg and were fed grass silage and 400g/day concentrate for 56 days, with the whole diet providing the equivalent of 60mg or 500mg of α-tocopheryl acetate/kg DM. Lambs were weighed and blood samples were taken weekly.

“At day 0, plasma a-tocopherol concentrations were low 0.8mg/ml and did not differ between treatments,” said Dr. Kasapidou. “Plasma α -tocopherol concentrations then decreased in all lambs except for those fed grass silage, which increased.”
At slaughter, muscle and liver a-tocopherol concentrations were in the deficiency range for lambs fed 30mg, 60mg or 120mg, whereas plasma creatine kinase and tissue polyunsaturated fatty acids were unaffected by dietary vitamin E level.

“But creatine kinase levels were higher and glutathione peroxidise levels lower in lambs fed grass silage compared to concentrates alone,” said Dr Kasapidou. “Muscle and liver α -tocopherol concentrations were 1.8- and 4.1-fold higher in lambs fed silage and 60mg of α-tocopheryl acetate than those fed 60mg of α-tocopheryl acetate alone.

“But there was less of a difference between lambs fed silage and 500mg/kg DM of α-tocopheryl acetate or just 500mg α-tocopheryl acetate in the concentrate, with muscle and liver differences of 0.4- and 0.7-fold, respectively.

“Tissue n-3 polyunsaturated fatty acid concentrations were higher and n-6 fatty acids lower in lambs receiving the grass silage compared to concentrate-based diets, but were not affected by dietary vitamin E level,” she added.

“Lower plasma and tissue levels of a-tocopherol are present in lambs supplemented with all-rac-α-tocopheryl acetate on a concentrate compared to a mixed diet of silage and concentrates, although growth can be achieved at tissue levels previously considered to represent deficiency, and this may affect the subsequent shelf life of the meat.”

full paper.pdf      

Kasapidou E, Enser M, Wood JD, Richardson RI, Wilkinson RG and Sinclair LA: “Influence of vitamin E supplementation and basal diet on the vitamin E status, performance and tissue fatty acid concentrations in lambs.”  Animal 3, 516-526
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