it can be expensive to have Cows calving throughout the year. Summer forage is used ineffectively, while in winter expensive supplements are needed to ensure a high conception rate and optimal weaning weight.
“It also makes effective selection for fertility difficult and complicates feed flow planning,” says Leslie Bergh from the Agricultural Research Council (ARC) Livestock Business Division. “Performance testing is complicated and pregnancy testing costs more.” A well-planned breeding season makes more economic sense. Leslie explains the best camps can be allocated to the breeding herds to boost conception rates. The cows can also be mated at optimum condition and weight.
The period when cows’ nutritional requirements peak (six to 14 weeks after calving) can be made to correspond with the peak production of forage. This will help cows maintain condition and increase weaning weights. High forage production will also correspond with the calves’ pre-weaning growth period.
The ideal time for calving is six to eight weeks before optimum green grazing is expected in summer, says Leslie. “The aim of a breeding season is to get the maximum number of females pregnant in a relatively short period, and as cost-effectively as possible. “The most favourable breeding season is the one enabling optimal use of the cheapest source of high-quality feed – summer forage. If a breeding and calving season starts late, calves will be born too small to utilise the high milk production from peak summer forage, lowering weaning weights.
On the other hand, the cows’ higher nutritional levels could also mean larger calves, and this could cause more calving problems.”
A well-planned season
In a well-planned summer breeding season, the period when cows need less nutrition after weaning corresponds with the low forage production in winter, says Leslie. Consequently, less supplementation is needed. Performance testing can be done more effectively because calf groups are larger and more uniform in weight and age. Non-pregnant cows can also be marketed in a good condition before the onset of winter.
“Planned breeding seasons also mean easier and more effective selection for fertility because sub- or infertile cows and bulls can easily be identified, as well as bulls with a low libido,” he adds. “It also means early culling of non-pregnant females – directly after pregnancy diagnosis – and helps identify early- versus late-calving cows.”
It’s important to choose a time of year when the cows are in top breeding condition – usually about three months after the month with the highest rainfall. “For a summer breeding season, the best conception is achieved if cows calve about one month before and up to one month after the first good rain has fallen,” he explains.
This means if the first good rain in an area usually falls in October, the cows should calve from September to November, implying a breeding season from November to February.These guidelines and recommendations are for summer rainfall areas and should be adapted accordingly for winter rainfall regions. (See: Bull/female ratio guideline).
One or two breeding seasons?
Leslie says bulls can be used more cost-effectively in two breeding seasons. Cows that have skipped pregnancy and aren’t culled can be remated sooner. This means they’ll only skip six months and not a full year. With two breeding seasons, heifers can be mated at 18 months, instead of the usual 24 months.
But Leslie warns having two breeding seasons could tempt farmers not to cull cows that have skipped conception. Contemporary groups will also be smaller, as the annual calf crop will be spread over two seasons. As routine management must be done twice a year, it’s more labour-intensive. A winter breeding season should only be considered if enough high-quality feed is available at affordable prices. If it’s expected that heifers will become too fat for mating at 24 months, consider mating at 18 months during a second breeding season.
But as a second season could put more stress on young heifers, only consider it if ample good quality grazing and/or crop residue, hay or silage are available during the winter following calving.Leslie proposes a breeding season no longer than 90 days. “Taking 285 days as the average gestation period, cows must conceive within 80 days of calving to calve each year at the same time,” he says. “A breeding season of 75 to 80 days is better than one of 90 days.”
The ideal is a 65-day (three oestrus cycles) breeding season for lactating cows and a 45-day (two oestrus cycles) breeding season for heifers and dry cows. For a high conception rate, cows need good nutrition and condition.Heifers and cows
Leslie explains the sound management of heifers and cows is crucial for ensuring a high conception rate. They need enough high-quality feed to grow during pregnancy and lactation and still reconceive.
Weight, body condition and growth are the primary indicators of when heifers can be mated, and are much more important than age. “The ideal is to breed heifers as soon as possible after sexual maturity,” advices Leslie. “This is usually when a heifer is at 60% to 65% of her expected mature weight. For medium-framed cows with an average weight of 500kg, the target weight of heifers for breeding is 300kg to 325kg. The target weight at the end of the summer breeding season is about 85% of the expected mature weight.”
If cows calved during winter aged about 30 months, they can be transferred to the main breeding season by waiting an extra six months before they’re mated again – giving them adequate time to recover. “The second option is to mate them immediately to calve again during winter at an age of about 40 months,” says Leslie. “This will eventually lead to two full breeding seasons.”AI can be used for the first third of the season, and bulls introduced for the rest of the time. Alternatively, use AI for one oestrus cycle and then introduce bulls. Using AI only is high-risk, and should only be considered if nutrition, management and AI practices are of a high standard.
Contact Leslie Bergh on 012 672 9145. |fw
