Weighing up the options

18 March 2016

Knowing critical mating weights and assessing body condition score – why are these skills so important?

At the ReproActive workshop in southern Victoria on Wednesday, cattle researcher Dr John Webb Ware, of the Mackinnon Project, explained why and showed producers how they could improve their herds’ reproductive success by using these simple measurements.

“A heifer’s first joining (as a 15-month-old to calve down at two) is the most important, it sets her up for the rest of her life,” John said.

“If heifers are initially late to join they remain late, which is why knowing your herd’s critical mating weight and being able to accurately condition score, to improve your reproductive outcomes, are such valuable skills.

“More heifers in calf also means more replacement females and an overall younger, more productive herd of greater value.”

Critical mating weight is the weight at which at least 85% of heifers become pregnant over a six-week mating period. It varies between breeds and even between herds.

“A good rule of thumb is that critical mating weight is about two-thirds of your mature cow weight,” John said.

“For British breeds this is generally considered about 320kg.”

Producers can work out their own herd’s critical mating weights by weighing heifers at pregnancy testing and taking note of what is pregnant, what is empty and their corresponding weights.

“In good years, producers may not be too concerned, however, in tougher seasons, knowing your critical mating weight provides forewarning as to whether a portion of heifers may need supplementary feeding to meet their target weight to ensure an 85% pregnancy rate, or to have contingency plans for more empties than usual,” John said.

Being able to accurately  condition score is a simple skill which, according to John, should be in every producers’ repertoire.

“Being able to accurately assess body condition score means producers can supplementary feed more efficiently and improve their herd’s reproductive success by ensuring females are in sufficient condition to calve, lactate and re-join within 365 days,” he said.

John said, as a guide, autumn calvers should be in a body condition score (on a scale of 1-5) of 3 to 3.5 at calving, while spring calvers can be a little lighter at condition score 3 knowing feed availability improves during the calving period.

“Autumn calvers tend to have less feed available so the extra condition is important to sustain the cow during early lactation and to ensure they are cycling adequately at joining to achieve acceptable pregnancy rates,” he said.

John said the skills of accurate body condition scoring and knowing your herd’s critical mating weight created numerous benefits across a beef business.

“By getting more heifers to puberty and cycling within that initial six-week joining period, producers are setting their females up for a successful reproductive life by improving their pregnancy rates, achieving tighter calving intervals (leading to more even calf drops and heavier weaners) and reducing dystocia,” he said.

More information: John Webb Ware T: 03 9731 2224 E: j.webbware@unimelb.edu.au

To find out more read the MLA More Beef from Pastures module on critical mating weights and reproductive success at http://mbfp.mla.com.au/Weaner-throughput/1-Maximise-live-calves

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