Heather Larson – 9/19/2011
In the last few articles you have seen a different focus on how to grow replacement heifers and possible a new target first service breeding weight. This may be of some interest for quite a few of you, but if you are not ready to try out some new research then lets revisit how we have always grown heifers.
Our first area of visitation is not to over feed your heifers. This may be difficult for some operations as their replacement heifers are not chosen until later in the back-grounding phase. Excess energy intake from 2 to 3 months of age until after conception should be avoided to reduce negative effects on mammary development. Studies have shown what seems like minimal differences in average daily gain (ADG) can impact mammary development. A study from 1984 showed that heifers gaining 1.17lbs/day before 8 months of age had higher milk productions compared to heifers gaining 1.42lbs./day. In addition to negative effects on mammary development, excess energy is extremely costly.
What should your heifers be gaining on a daily basis? This really depends on your cow size. It has always been said that heifers should weigh 60-65% of their mature size before the breeding season. In fact studies show that Bos Taurus(Continental) breeding weights are 60% and Bos indicus(eared) breeding weights are 65% of mature weights. Even more recent studies have shown that genetic advancements may be moving to a lower percentage. With all that being said, I am going to use 60% of the mature weight for a target point at breeding. Let’s say your average size of your cow herd is 1350 lbs. That means you want your heifers weighing 810lbs. by breeding season. The heifers are weaned on October 20th at 550lbs and the breeding season begins on June 1. You have 220 days to gain 260lbs. That means the heifers need to gain an average of 1.18lbs./day.
When you think about rations that calves are weaned on, they typically are a 43Mcal ration or a 45Mcal ration. A 45Mcal ration will probably have a 1.75lb ADG to 2lb. ADG. This already is too much energy and a waste of money. If you wean on a 43Mcal ration then you may be a little closer to what you need to get to 60% of mature size without wasting feed. However, it may be more cost effective to reevaluate your weaning ration and utilize a lower Mcal ration to be cost effective and grow those heifers to 60% of their mature weight.
Waiting longer than you have to, to establish a growing heifer ration is money out of your pocket and potential damage to your replacement heifers. Knowing where your end weight is and what you need to gain to make it there are the numbers you need to establish the correct ration for those replacement heifers.
Fore more information view Managing Change in Livestock Production.