Are your replacement heifers ready to breed? You still have time to change their condition before breeding time. This is the time to assess their present condition and determine if the ration needs to be modified to allow them to hit the target breeding weight.
What is the ideal size/weight/condition for replacement heifers? The literature I grew up with was 60% or 65% of mature weight for British versus Continental Breeds. However, recent research has indicated the replacement heifers can be bred at 50 to 55% of mature weight. I have seen a wide array of heifers at breeding time from heifers over 1000 pounds looking like a finished steers to less than 500 pounds looking a little too much like a freshly weaned calf. Neither of the extremes would be ideal for most producers.
What is 55 to 65% of mature weight? You can find these estimates in Table 1. First, you need to know the average size (pounds) of your mature cows. If you don’t have a scale, the next best option to find the weight of your mature cows is cull cow weight. Let’s say your cows weigh 1350 pounds and you want them at 60% of mature size of breeding time. So, the replacement heifers should be weighing 810 pounds at breeding.
Research has shown that heifers reach puberty around 55% of mature weight and heifers weighing from 50 to 65% of mature weight will have adequate reproductive performance over the breeding season. However, more heifers conceived in the first 30 days of the breeding season when they were developed to 55 compared to 50% of mature weight, and heifers developed to 65% of mature weight cycled back sooner after calving compared to heifer developed to 55% of mature weight. Furthermore, all replacement heifers should be at 85 to 90% of their mature size at calving time no matter the percentage of mature weight at breeding time. You will have to determine the nutritional program from breeding to calving.
Over- and under-weight replacement heifers can impact the producers’ bottom-line with open heifers. Underdeveloped heifers and over-conditioned heifers may have lower conception rates. However, over-feeding also cost money and may not be necessary to hit good breed up. In today’s market, prices for open heifers have reduced the sting on open heifers. However, many producers are only getting a limited number of replacement heifers due to high calf prices, so open heifers may reduce the producer’s cowherd size.
Source: Julie Walker