The sexual maturity of heifers is weight dependent. To get heifers in estrus and inseminated, so they can calve at around two-years of age, it is crucial that the animals enjoy optimal health and feed intake in their first months of life. If heifer feed intake is not assured in all age groups, this tends to typically result in a higher age at first calving. Too much nitrogen in the feed that increases ammonia concentration in the plasma, can possibly inhibit both appetite and the secretion of reproduction hormones. Research has shown excess nitrogen has a negative effect on feed, on both follicle development, fertilisation and embryo survival.
Classifying the problem
The growth and height of calves should be monitored. A number of illnesses in the first few months of a heifer’s life, affects feed intake and should therefore be prevented. Check that 1st calf, 2nd calf and older cows are doing well after calving. Thin manure (manure score < 3) is however a sign of inadequate processing of the feed in the gastrointestinal system.
Both permanent and sudden changes in feed intake, can affect ovarian function in heifers. Certain research shows that an increased urea concentration in the plasma, has a direct adverse effect on the egg within the follicle and results in the development of poor quality embryos. Other research shows that an increase in the allocation of ruminant protein can increase the number of days to first insemination by exacerbating the negative energy balance, as the cow has to expend more energy in secreting excess nitrogen. Provided the level of urea in the milk is within the recommended 3-5 mmol/l, this will have no adverse effect on reproduction.
Points for action plan
Keep a close eye on how feed rations are adapted to the physiological needs of the heifer/cow, via feed planning and feed management. Specific attention ought to be given to the feed intake of new calvers.
- Adequate and balanced supply of energy and protein for heifers and cows - including when grazing.
- The urea level in milk as an indicator whether protein allocation is a strain on the animal.