Research Roundup is designed for farmers who want to keep on the cutting edge of new research, with the understanding that ‘new’ information includes ‘ideas that are yet unproven’. The newer the science is, the more uncertain we are about the results – so take what you read with a pinch of salt. With this in mind, we can still report on what researchers are thinking, giving us some idea of where we might be heading into the future.
- Analysing a nation’s dairy breeding preferences – three farmer types emerge
- Enhancing bull libido using chemicals found in cow urine
- Can we use early hormone tests in heifers to predict productive longevity?
- Factors influencing maternal egg quality in dairy cows
Source: AbacusBio Ltd, Australian Dairy Herd Improvement Scheme and the Department of Economic Development, Jobs, Transport and Resources (Australia & New Zealand)
Breeding indexes have had great uptake in countries such as Ireland and New Zealand, where farming systems are mostly homogenous and farmers can agree on what defines ‘the perfect cow’. But how well do they work in an industry where climate varies wildly due to the sheer size of the country-continent, where six different systems can thrive side-by-side, when farm size can vary from tiny fifty-cow dairies to multi-thousand megaliths, and farming philosophies lead to brawls at the local pub? (I’m talking about Australia, of course.)
In this paper, researchers have tackled this thorny problem and have come up with a solution: ask the farmers what they want, identify trends in their preferences, and then release multiple new indices that match different needs. Under this philosophy, ADHIS have just released three new indices – one for each broad type of farmer that makes up the Australian dairy industry. This paper details the research and data collection efforts that went into the new indices, and the analyses behind farmer type.
The method was statistically very thorough. Each one of Australia’s 6,314 dairy farms was given the opportunity to contribute to results, and 551 farmers completed the survey. Two hundred of these were chosen at random, so that the data does not just come from those interested enough to float their opinion. Farmers were asked to rank 13 traits (nine traits that were already included in the old Australian Profit Ranking or APR and four new ones). By correlating these results to demographic information, the researchers were able to identify three different types of farmer.
Production-focused farmers placed a heavy emphasis on longevity, feed efficiency, and protein yield. They tended to be older in age. Functionality farmers focus on mastitis, lameness, calving difficulty and fertility. Type farmers had a strong preference for mammary system and (obviously) type – these had more breed society-registered herds (which makes a lot of sense) and were on the younger side.
These new indices have given consideration to farmer preference, rather than focusing purely on economic benefits of different traits. It is hoped that this will improve the suitability of the three new indices, which can be read about on the ADHIS website.
Enhancing bull sexual behaviour using estrus-specific molecules identified in cow urine
Bull libido is highly variable, and ‘low-performing’ bulls make semen collection difficult for AI production centres. These bulls often result in technicians taking increased risks and time to excite low-libido bulls (leading to lower workforce efficiency) and lead to a reduced number of semen doses, impacting the industry.
Natural courtship between bull and cow usually involves chemical communication in addition to more obvious auditory, visual and tactile stimuli. The objective of this study was to isolate these chemicals and see if they could be used to enhance bull sexual activity. Researchers isolated four of these chemical compounds from cow urine and vaginal mucus, and then incorporated each of them in different nasal sprays at four different bull collection centres around France.
Researchers found that two of the compounds enhanced libido in bulls after inhalation, and the other two were found to also increase sperm concentrations in ejaculate after use. The spray is now being developed for commercial use.
While it’s hard to imagine commercial dairy farmers giving their bulls a nasal spray each day to ‘boost’ performance, the research does shed some light on the animal behaviours we observe in the paddock. Every farmer has stories about ‘strange’ bull behaviour – bulls that fixate on one cow and ignore the others, bulls that seem to have little interest in the task at hand, and bulls that harass other bulls. It’s hard for us to account for chemical attraction, but these results prove that there’s certainly something going on which we aren’t able to see.
Source: Michigan State University (USA)
If there was a test for telling early on which heifers are going to have long productive lives, and which ones are going to drop out early, then would you use it? This may be a possibility in the future, according to the results from this paper.
Anti-Mullerian hormone (AMH) is produced by ovarian follicles and is already used as a predictor of success in IVF programs for women. AMH levels provide a guide to ‘ovarian reserve’, the capacity of the ovary to provide egg cells that are capable of fertilization resulting in successful pregnancy. AMH levels in cattle have also been linked with follicle counts, ovarian function and general fertility.
According to previous research, approximately 25% of cows have relatively low levels of AMH. By weeding out these cows early (which we would expect to have sub-optimal fertility), we could hypothetically save money on unnecessary rearing costs (ranging anywhere between $1600 to $2200 per heifer in Victoria) by removing these from the herd.
In this study, researchers took a single measurement of AMH in 11- to 15-month-old Holstein heifers, and then compared this to their health and performance results over two lactations. They found that heifers with low AMH concentrations had, on average, a shorter productive herd life (by 196 days) and a reduced survival rate after birth of the first calf, compared with age-matched herd mates.
This is an interesting result which could point to a future longevity test for heifers. However, as this was performed on a single herd with only 281 animals, more research will need to be done (under Australian conditions) before concrete recommendations could be made. And as always with potentially expensive tests, an economic cost-benefit analysis should be done to see if the results are worth the costs.
Source: Shanghai Jiao Tong University (China)
Conception does not always lead to pregnancy. Conception is defined as fertilisation and implantation – when sperm fuses with egg and then settles into the uterus. From there, it has a very long way to go before it becomes a living, bawling calf – a process involving cell division, organ development and embryo maturation.
Many never make it to this stage. According to this review, 90% of eggs are fertilised but the average calving rate is only about 55%, suggesting that 35% of fertilised eggs die at the embryo/fetal stage. Most (70-80%) of these losses occur between days 8 and 16 after insemination, too early to detect with normal pregnancy testing methods. This means that even with early pregnancy testing, these losses appear as failures of insemination when viewing herd records and are invisible at a farm level.
Although much has been made of sperm quality, egg (or ‘oocyte’) quality is equally important for successful embryonic development. In this paper, researchers have tried to list what factors contribute to improved maternal oocyte quality in the hope that we will better be able to improve embryonic development.
The paper itself is enormously comprehensive, so if this is your jam, I would strongly recommend reading the whole thing. However, for a quick and dirty list, I’ve split factors into two groups below.
Factors that are NOT visible at a farm level
- Malfunctions in maternally-inherited cell machinery. These include:
- Maternal mRNA – genetic material from the mother that regulates development in the embryo
- Mitochondria – tiny organs whose job is to produce energy for the cells. Mitochondria can be affected by factors such as maternal nutrition, alterations in temperature, maternal age and maternal genes.
- Regulation of maternally-inherited components by other factors
- MicroRNA (sections of genetic code that regulate genetic expression)
Things that ARE visible at a farm level
- Maternal age
- Oocytes from heifers that have not yet reached puberty do not develop as well as oocytes from adult cows
- Female fertility declines past 13 years of age in cattle (and 35 years of age in humans) resulting in decreased fertilisation rates, abnormal fertilisations, arrested embryonic development and spontaneous abortions
- Maternal nutrition
- Follicles need nutritional support to successfully complete growth and development. This includes a diet balanced in vitamins and minerals, including trace elements such as zinc, copper and manganese.
- Under-nutrition: cows with low body condition scores have more abnormal oocytes and reduced development rates. Cows in negative energy balance have lower conception rates and a higher incidence of early embryonic losses.
- Over-nutrition: high energy diets have been found to reduce oocyte quality in high-yielding dairy cows, possibly because of excess circulating insulin and insulin resistance. Oocytes are smaller in obese mice compared to lean mice, and have been found to self-destruct more often. Diets high in crude protein (17 – 19%) fed during early lactation can also cause poor embryo quality due to high blood urea concentrations.
- Heat stress
- The mechanisms behind why maternal oocyte quality declines over summer are not fully understood. There is some evidence that this could be due to membrane changes, alterations to genetic expression and other disruptions to cell structure. Heat stress is thought to damage pre-ovulatory follicles as well as dominant follicles, meaning that it takes several oestrus cycles after a heat stress event before fully-functional follicles are present.
- Heat also reduces feed intake, leading to poor nutritional factors as described above.
Maternal age, nutrition and heat stress are factors that we should already be managing on farm. However, the paper stresses the importance of getting these things right in order to enhance maternal reproductive performance. As we start understanding things better on a cellular level, the hope is that we can find additional ways to manage oocyte quality and reduce early embryonic losses.