Heifer management
Heifer fertility
Improving heifer fertility is one of the most cost effective strategies for improving overall herd performance and business profitability.
First calf heifers (heifers being remated the year after first calving) tend to have the lowest reproductive performance of all classes of breeders. This is because they are still trying to grow while raising a calf. As lactation is the highest biological priority heifers on inadequate nutrition will lose body condition. If body condition becomes too low the heifer will not be able to cycle or reconceive.
Critical mating weight
Critical mating weight is defined as the weight at which 85% or more heifers will become pregnant in a 42 day joining period. The critical mating weight for Bos indicus heifers is heavier than that of Bos taurus breeds. Critical mating weight ranges from 280-340kg, although the majority of Bos indicus heifers will need to be between 320-340kg to conceive.
Supplementation can be used to manage body condition and weight. If protein supplements are fed pre-calving, the program must continue until the season breaks and good quality pasture is available. Spike feeding a high quality protein supplement for 6-8 weeks before calving has been shown to increase reconception rates. However, the economics of this strategy need to be fully assessed before implementation.
Post partum anoestrus interval
The period between calving and resumption of cycling is known as the post-partum anoestrus interval (PPAI). The main factors influencing PPAI are nutrition and lactation. The PPAI in Brahmans is often longer than that of Bos taurus breeds when nutrition is poor. However, when in good condition Brahman heifers can reconceive within 61–65 days, allowing for a calf every year.
In order to maximise body condition and for heifers to have the best chance of reconceiving, calves should be born close to the expected break of season. This will allow peak milk production, peak demand for milk and peak pasture nutrition to align.
Calving difficulty also increases PPAI. This is probably due to stress, injuries and general recovery time required. The most common cause of dystocia (calving difficulties) in heifers is having a calf that is too large to fit through the underdeveloped pelvis. This problem is less common in Bos indicus breeds but can be a problem in Bos taurus and Bos indicus-cross heifers.
Segregating heifers
If possible, heifers should be segregated from the general breeder mob from weaning until at least the start of their first joining period. Ideally, segregation should continue until the first calf has been weaned. This allows for targeted management such as strategic supplementary feeding and optimising the timing of calving. When possible, heifers should be run in paddocks with the best available pasture. Phosphorus should be fed in the wet season in phosphorus deficient country.
Bulls
Select bulls with low birth weight Estimated Breeding Values to prevent dystocia. Young bulls are less likely to carry diseases such as vibriosis that can cause calf losses. Vaccinating heifers against diseases such as pestivirus and vibriosis can reduce calf losses. Bulls should also be vaccinated.