Despite this challenge, there are opportunities for producers to capitalise on and to maximise heifer and cow pregnancies within controlled mating periods.
“Nutrition is a major driver of fertility, which is important in southern systems where we expect to join heifers at 15 months and clave them down at two years,” said cattle consultant Rod Manning.
“If nutritional demands are not met, body weight and reproductive capacity are sacrificed first. Females need energy to switch on their reproductive cycle, or in the case of heifers, reach critical mating weights to stimulate puberty and cycle.”
Genetic selection
Manning, who will be speaking at Meat & Livestock Australia’s (MLA) More Beef from Pasture ReproActive Workshop on Wednesday, suggested that if producers are concerned their cows wouldn’t reach critical mating weights, then they should consider feeding their cattle early. “If you think your weaner heifers will struggle to make that 300-320kg target at 15 months, plan early to increase their energy intake.”
Critical mating weight is the weight at which 85% of a herd is pregnant within two cycles. “Failing to do this will affect growth, particularly pelvic development, delay puberty, increase the risk of dystocia and lead to fewer pregnancies within that six-week joining period,” advised Manning.
As a result of more focus being placed on higher growth rates for younger cattle, Manning highlighted that genetic selection had helped increase the critical mating weights of maiden heifers during the past decade.
Weaning time ‘critical’
“It used to be 260-280kg, now with larger cattle, it’s more like 300-320kg. We really want them at 320kg at joining so they are about 440kg at the point of calving.”
Another key point that was raised by Manning was to look after younger cattle, as they are most at risk during challenging situations. “They have to have enough nutrition post calving and adequate body condition to ensure that they return to oestrus quickly enough to get back in calf,” he said. “They require energy for maintenance, growth, lactation and reproduction and, once the body condition score falls below three, it’s a slippery slope.”
Accurate body condition score is also an important aspect of running a successful operation. “Body condition score three is the sweet spot we should all be aiming for,” added Manning.
The correct time of weaning is recognised as being critical to a producer’s business. Once a cow begins to slip in condition, below body score 3, a weaning date should be set.
Calves need good feed
“Running a cow-calf unit when the season is tough and feed is scarce is the most inefficient use of the pasture available,” claimed Manning. “By weaning calves at four-and-a-half to five months, a cow’s energy requirements are halved, she can be treated as a dry unit and calves given priority for feed.
“In severe dry conditions, calves can be weaned at a minimum of 100-120 days old and about 120kg but you need to be a very good nutritional manager to attempt this.
“The calves will require high-quality feed, about 10.5 to 11 of metabolisable energy in the form of pellets or grain and very good silage or Lucerne.”
Finally, maiden heifers should be joined for six weeks and cows for six to eight, regardless of seasonal conditions, according to Manning. “Don’t be tempted to leave bulls in for longer,” he warned. “If they join later, you never get them back and this leads to uneven calf drops, lower average weaning weights and fewer replacement heifers making their critical mating weights.”