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MANAGE REPLACEMENT HEIFERS FOR FERTILITY AND PRODUCTIVITY IN HERD

by: Dr. Mel Pence
University of Georgia College of Veterinary Medicine with Myra Burnsed, Jennifer Carter, Suzanne Sheldon, Kendrick Sudderth (UGA College of Veterinary Medicine class of 2008)

Incorporating the following practices into your management of a heifer replacement system can be effective tools to increase the overall fertility and productivity of your herd, both in the short term and in the future. Within the beef cattle industry, the devotion of time and resources to the reproductive efforts in a herd holds tremendous potential for a significant increase in revenue.

Phenotypic Selection

The first step to developing quality heifers is to choose those that will best support the breeding goals of your program. This requires consideration of the genetic and phenotypic qualities you want to perpetuate.

Generally speaking, a producer should match their cows to the environment and their bulls to the market. In choosing heifers to keep for a development program, it is important to evaluate the heifers individually, yet also as a collective group. Within the replacement group the producer should aim for uniformity in the cow base, which will result in a more uniform calf crop each year.

On the individual level, potential heifers can be evaluated using a combination of conformation, general appearance, disposition and frame score. The frame score is calculated mathematically from measurements of their hip height, age and weight. Once the genetic and phenotypic selections have been made, the following steps can be addressed to narrow down the replacement herd to the final number, and work to increase their fertility.

Adequate Nutrition and Appropriate Body Condition Score

A critical element for increasing the reproductive ability of replacement heifers is establishing an adequate body weight through appropriate nutrition. Heifers require an increased level of nutrition compared to established cows due to the demands of maintenance as well as growth. Those metabolic needs must be met and surpassed in order to create a positive energy balance to support the demands of reproduction.

Heifers should be at a body condition score (BCS) of 5 to 6 at the time of breeding and a BCS of 6 at the time of calving. Along those same lines, a heifer should be at 65 percent of her adult body weight at the time of breeding and 85 percent at the time of calving. These adequate levels indicate a physiologic ability to support the energy needs of breeding and pregnancy.

Reproductive Tract Scoring and Pelvic Measurement

Your veterinarian can play a crucial role in helping to select heifers that are reproductively sound. Reproductive tract scoring is a method that determines a heifer's stage of puberty 30 to 60 days prior to breeding. The scale of 1 to 5 is based on the size of the uterine horns, the ovary size and the presence and size of ovarian follicles or presence of a CL.

These elements give clues to the stage of her cycle. A heifer with a CL present on large ovaries and a uterus with good tone is considered a 5 and has reached puberty. Heifers with no uterine tone, small ovaries and no palpable follicles are a 1, and have not yet begun to cycle. Varying follicle sizes fall in between.

Those heifers with the highest scores should be kept for replacements, as they are either currently or close to cycling and thus will be ready for breeding earlier. The higher the reproductive tract score, the more likely a heifer is to become pregnant early in the breeding season.

Pelvic measurement can also be employed at the time of palpation to determine the size of the pelvis. Horizontal and vertical measurements are used in a mathematical calculation. The number produced helps determine if the heifer has a small pelvis relative to her size.

The ability to cull out those heifers with small pelvic measurements can drastically reduce the incidence of calving problems (dystocia) due to small pelvic size. Fewer dystocias reduces potential economic losses due to cow and calf losses. By paying a veterinarian to perform reproductive tract scoring and pelvic measurements, you increase your reproductive efficiency and reduce the number of calves you have to pull.

Feeding Monensin to Trigger Early Onset of Puberty

Monensin, a feed additive, should be included in the heifers' ration following their weaning. Monensin functions indirectly as a partitioning agent; it helps the heifer determine how she will use feed. The normal order in which a cow would utilize food resources is first for body maintenance, second is for growth, third for milk and the last thing is for reproduction.

Energy utilization is impacted by a protein produced by fat cells in the body called leptin, and monensin helps leptin work. This is why feeding monensin will reduce the age at puberty by nearly three weeks, resulting in more heifers becoming pregnant earlier in the breeding season.

Additionally, feeding monensin reduces the consumption of feed by 10 percent while maintaining the same weight gain and reproduction. By adding monensin to a balanced ration the heifers should reach puberty at an earlier date and more heifers should settle early in the breeding season.

Early Breeding Season for Heifers

Why do heifers need a head start? The investment in heifer development is great and we need to ensure the maximum number of heifers rebreed with their second calf. To improve reproductive efficiency in your herd breed heifers about 30 days before your cow breeding season starts. This has long reaching significance as first calf heifers have a longer post partum anestrous period before they can be bred back for the second calf.

By breeding the heifers early for their first calf, the second calf breeding should likely coincide with the mature cow breeding time frame. Additionally, heifer's calves are usually smaller than those from a mature cow and the extra month of growth allows them to catch up with the other calves for a uniform calf crop.

Key points:

1. Select heifers that will thrive in your environment and management.

2. Feed heifers to attain 65 percent of mature weight at breeding in a body condition of 5 to 6.

3. Use reproductive tract scoring and pelvic measurements to select heifers for the breeding herd.

4. Feed monensm to improve percent of heifers settling early in the breeding season.

5. Breed heifers 30 days before the cow breeding season starts.

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