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To use AI more successfully producers must breed, feed and house their cattle 'appropriately' to avoid clinical stress. That was the conclusion of a study, carried out by a team of scientists led by Hilary Dobson at the University of Liverpool, examining why is it getting more difficult to successfully AI cows
"Animal husbandry has failed to keep pace with improved genetics for yield," Professor Dobson told delegates at the British Society of Animal Science's international conference entitled: Fertility in dairy cows - bridging the gaps.
As milk yields have risen, first insemination pregnancy rates have fallen. The percentage of cows standing to be mated has also fallen - from around 90% in 1960 to around 55% in 2007 - as yields have risen and oestrus duration is also shorter in cattle today.
"Add to this the decline in labour on dairy units and it's not surprising that fewer cows are being inseminated at the right time and with a declining degree of success."
Milk progesterone profile studies also revealed more 'atypical' profiles and there are several cow health and management factors that are disrupting fertility and increasing the period of time between calving and pregnancy. Caesareans, for example, increase this interval to around 140 days, lameness to around 120 days and endometritis to around 115 days, compared to the desired interval of around 85 days.
"Stress caused by other production diseases, such as mastitis, also have a detrimental effect on fertility and the success of AI. Stress disrupts reproductive hormones," said Professor Dobson. "Preventative husbandry can go someway to making it easier to successfully inseminate cows. But breeding also has a role to play. Emphasis is still very much on production in most countries, and away from durability, and health and reproduction.
"More emphasis on the latter in cattle breeding indices, similar to the Danish selection index, is the way forward to help avoid clinical stress and improve fertility and AI success."
As the incidence of uterine disease in UK herds continue to rise, fingers point at E coli - the most commonly isolated uterine pathogen, which often precedes infection with other organisms. The constituents of the cell wall of this gram-negative bacteria - that form a lipopolysaccharide or LPS - can be detected in the uterus, peripheral circulation and in follicular fluid of infected cows. And this affects the physiological function of uterine and ovarian cells.
"And this means that prostaglandin production is affected, and aromatase expression and estradiol production is down regulated," Erin Williams, from London's Royal Veterinary College told delegates at the British Society of Animal Science's international conference entitled: Fertility in dairy cows - bridging the gaps.
"These mechanisms may be partly responsible for the sub fertility in post partum dairy cows," added Dr Williams.
This is bad news for UK dairy producers as uterine disease in cattle is increasing. The incidence stood at around 4,000 cases requiring direct intervention by a vet in 2003 to almost 6,000 cases in 2006.
Clinical uterine disease, or endometritis, costs the dairy industry millions of pounds each year due to longer calving intervals, an increased number of services per conception, and increase in the number of culls and subfertility.
"High numbers of bacteria in the postpartum uterus result in reduced growth and function of the first postpartum dominant follicle," said Dr Williams.
"Ovarian follicles grow slower and produce less estradiol - and corpora lutea grow slower and produce less progesterone - in cows with higher numbers of uterine pathogens."
Extending dairy cow lactations could not only boost profitability, but it could also offer improved levels of health and welfare for European herds.
That was the conclusion of a study, carried out by Chris Knight from the University of Copenhagen, which set out to answer the question of whether extended lactation could work for European dairy producers.
"For a 100-cow herd, extending lactations would incur costs of £22,000, but generate £42,000 in extra revenue, resulting in £20,000 in extra profit," he told delegates at the British Society of Animal Science's international conference entitled: Fertility in dairy cows - bridging the gaps.
"And trials and data show that increasing the voluntary waiting period between calvings does not increase disease incidence per lactation and this means that, on an annual or lifetime basis, disease is reduced," added Mr Knight.
He said that modern dairy cows could lactate for at least 18 months in the US, but cautioned that the US data was possibly influenced by BST. "Persistency is key here if we're to extend lactation length and there are three strategies to help improve this: breeding for increased persistency, identifying individual cows within the herd that are persistent and delaying their re-breeding, and/or managing the whole herd for increased persistency."
The latter, without the assistance of BST, would require a combination of more frequent milking and more appropriate nutrition, according to Mr Knight. In an experimental study at the Hannah Research Institute, involving 24 cows, the effect of milking frequency, nutrition and calving season were monitored during two consecutive 18-month lactations and persistency was altered by management.
"And rebreeding results were similar to non-extended lactation cows, although the reproductive problems at nine months were different to the 'usual' two-month problems. We think they may be less intractable," added Mr Knight.
Calving animals at less than two years of age does not reduce reproductive performance or productivity and, therefore, it could increase herd profit through reduced heifer rearing costs.
That was just one of the findings of a study, examining the factors affecting heifer survival and fertility on commercial dairy farms, presented to delegates at the British Society of Animal Science's international conference entitled: Fertility in dairy cows - bridging the gaps.
The work, completed by researchers at London's Royal Veterinary College, also revealed that heifers showing poor fertility before their first calving continue to have poor reproductive performance and poor productivity.
"But careful reproductive management of nulliparous [never calved] animals can influence productivity and profitability," Claire Wathes told delegates.
Juvenile predictors of adult performance were assessed by taking newborn heifer calves and measuring their size and metabolic parameters during rearing. These heifers were monitored from birth through to the end of their second or third lactation.
The effect of genotype, heifer rearing system and age and weight at the start of their first lactation on fertility, productivity and longevity were then assessed.
The research highlighted, for example, that maiden heifers that failed to conceive were significantly smaller, in both weight and height, at nine months old than there more fertile herd mates. Heifers that calved at between 22 and 23 months old required fewer services per conception compared to heifers that calved for the first time at between 24 and 25 months old - 1.1 services and 1.4 respectively. And 93% of heifers calving at between 22 and 23 months old were PD positive to first service, compared to 73% of heifers calving at between 24 and 25 months old. "Heifer rearing methods are very variable on UK farms and many potential replacement heifers never become productive," adds Professor Wathes.
"There is often little veterinary input during the rearing process and, in practice, growth rates of individual animals on a farm vary considerably."
Feeding fatty acids enhances reproductive performance, although some sources appear to be more beneficial than others. And when looking at fatty acids (FAs) and different fat supplements it is important to realise that different families of FAs impact on the cow's reproductive processes via different pathways.
These were just two of the take-home messages from Adam Lock, from the University of Vermont in the US, during his presentation at the British Society of Animal Science's international conference entitled: Fertility in dairy cows - bridging the gaps.
His paper asked the question: Can dietary fatty acid supplementation aid reproduction? "Extensive metabolisation, by the rumen bacteria, has made the study of dietary FA effects on reproduction challenging," he said. "And the specific mechanisms by which lipids/FAs impact on overall pregnancy rates have not yet been fully explored and understood," he explained.
"More research needs to be done to better identify the most effective fat sources, whether from seeds, oils or ?inert/protected' sources."
Feeding fats to aid dairy cow reproduction is of considerable interest at this time and this interest is based on several factors. These include the reduction in reproductive performance of dairy cows, which has driven the development of nutritional strategies to reverse this trend, and the fact that the use of dietary fat supplements will intensify as nutritionists strive to increase the energy density of diets to meet the requirements of the high yielding dairy cow.
"A variety of fat supplements have a beneficial effect on conception rates in lactation dairy cows and fats often improve pregnancy rates, although there is large variability in the responses observed. But the results are rarely negative," said Dr Lock.
Improvements are thought to be as a result of the FAs meeting the animals' essential FA requirement in early lactation and through the development of healthier ovarian follicles. Feeding FAs is also thought to improve the quality of the embryos produced and to reduce embryonic mortality through suppression of uterine PGF2α.
"Most data indicate that improved calving rate of fat-supplemented cows have been associated with an improved progesterone status of the cow. This increases the performance of the dominant follicle and corpus luteum and also helps the corpus luteum to survive and continue to produce progesterone during early pregnancy," said Dr Lock.
"The size of the dominant follicle is often larger in lactation dairy cows fed supplemental fat." FA supplements have also been shown to improve fertilisation rates and embryo development.
"In a trials with ET cows and heifers, the diet of the donor animal was more important that the diet of the recipient, suggesting that the dietary fat helps the cow to develop a robust embryo." So, when should producers begin FA supplementation? "Ideally at least 28 days, preferably 40 days, before breeding. And feeding FAs pre-partum may also benefit reproductive tissues and health."