Managing your heifers

GROWING HEIFERS TO LIVEWEIGHT TARGETS

We all know heifers are the foundation of the future breeding herd. They represent a significant proportion of the dairy herd and a high contributor towards total cost of producing milk.

Regularly weighing heifers is one of the most useful strategies to maximise potential lifetime production. Liveweights will give an accurate prediction of meeting growth targets and determine if intervention is required.

There are different growth patterns throughout the rearing phase for Holstein-Friesian, Kiwi Cross and Jersey heifers, so it is better to focus on heifer weight-for-age targets. Fertility and puberty are linked to weight, not age, so reaching pre-mating targets at 15 months optimises conception rates and allows heifers to calve earlier.

As a general rule of thumb, heifer liveweight targets (LWTs) are 30-60-90% of mature weights at 6-15-22 months of age. Mature liveweights can be estimated using breed averages, or more specifically using liveweight breeding values (Lwt BV) for your herd.

Heifer pre-weaning and weaning management is equally important for a great start to life but is not covered in this article.

Weight records can be uploaded directly into MINDA Live. Information is then easy to interpret with graphs to show if average mob weights are sitting above, below, or on-target. Although this sample farm was monitoring weights regularly, average weights were starting to slip in February and by April average weights were 45kg below target.

Using MINDA Live, further analysis of individual weights revealed >80% of the mob were underweight at 21 months of age. With PSC only 3 months away, there was little time to remedy this situation. It is likely these animals will struggle to hit pre-calving weights, with flow on effects into the mating period.

Regular weighing will allow you time to make corrections before critical time points such as pre-mating, pre-winter and pre-calving.

Heifers grown to a target liveweight are more likely to meet BCS targets at calving which means higher milk production and improved performance in the first lactation. Ideally, heifers should calve in the first 6weeks since they typically take 2 weeks longer post-calving to start cycling again. Earlier calving heifers are then more likely to calve early in the following season as well as conceiving to AB at their second calving which will improve herd genetic gain.

First calving heifers need to be managed carefully to reduce impacts on reproductive performance. An Infovet analysis of the 3-week submission rate for heifers across farms in our district shows on average, heifers are achieving an 86% submission rate within the first 3 weeks, but only 43% of farms are meeting targets.

A recent study reported in the Journal of Dairy Science also supports the body weight of heifers is positively associated with reproduction and length of time they remain in the dairy herd. Probably no surprises here, but the facts say it all. Nearly 200,000 NZ dairy heifers were studied over 3 calving periods; 92% calved for the first time at age 2, 76% a second time at 3 years but only 61% at 4 years of age. That’s a huge loss with poor reproductive performance likely to be the major cause of cow removal from the herd.

Sadly, these statistics show many cows are culled before the end of their second lactation and struggle to get back in calf.

BCS is a measure of a cow’s fat reserves and therefore an indicator of a cow’s energy balance. BCS is especially important during early lactation since it forms a buffer to balance energy demands against milk supply. Heifers typically lose more body condition post-calving as they utilise more energy to continue to grow and lactate. Dairy NZ recommends cows should not lose more than 1.0 BCS between calving and mating. This means older cows should have pre-mating BCS > 4.0 and 2 & 3 year olds should have BCS > 4.5 at mating.