Fertilisation failure is higher than previous estimates
Take Home Message: More than 50% of inseminations fail to fertilise, but this figure can be improved by reducing the extent of negative energy balance in early lactation.
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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