Reproductive technologies such as AI and embryo transfer (ET) are excellent methods to improve the genetics of your herd. However, whether due to cost or labor requirements, neither technology is widely used in the beef industry. Less than 10% of all beef cows are bred using AI and far fewer producers use ET.
Constraining the use of these technologies is the inconsistent success of either program. The most common sources of failure in AI and ET programs are improper protocols, not adhering to the protocol, inability to detect animals in estrus and incorrect technique. However, many producers who successfully employ the protocol still fail to get cattle pregnant. Nutrition is often overlooked in these situations and, while the animals may appear to be in good condition, significant problems may exist.
The most accurate way to assess nutritional status in cattle is to evaluate body condition score (BCS). In order to rebreed in a timely fashion, a heifer should have a BCS of 6 and a mature cow should have a BCS of at least 5.5 prior to calving.
Energy and hormones.
Balancing rations for nitrogen (protein) and energy is the key to a successful AI or ET program. Both technologies rely on a cow producing at least one viable oocyte (egg). In order for the cow to do so, she must resume estrus, which requires a ration that meets her energy and protein needs. First-calf heifers require an 11% protein ration and cows require a 10% protein ration, with adequate energy.
Energy is important in breeding females because certain hormones (i.e., insulin) are increased by
energy consumption. These hormones signal the body to resume estrus and produce oocytes. This is especially important to cows in ET programs. Supplementing donor and receipt cows with a small amount of starch can help boost insulin and other hormone levels to increase embryo yield and viability.
While inadequate nutrition is detrimental to AI and ET success, overfeeding can be equally, and perhaps more, problematic. In ET programs, many donor cows are overconditioned because they do not have a calf every year. Rations that provide excess protein and energy can reduce embryo viability and pregnancy rates.
Cows handle excess nitrogen (protein) by producing ammonia and converting it to urea, which is excreted in the urine. Cows are more susceptible than heifers to the negative effects of high-protein diets because their rations are often lower in energy and they require less protein, leading to a greater excess in the body.
When ammonia levels increase, the acidity of the blood increases, leading to acidity in the uterus and reducing the viability of sperm and embryos. For example, a cow in superovulation for ET may respond well but yield few fertilized embryos. It’s possible that there was too much protein in her diet, compromising sperm viability. If there is a high percentage of degenerate embryos, perhaps their viability was compromised by the acidity of the uterus.
As a rule of thumb, balance cow rations for less than 12% to 14% protein and heifer rations for less than 15% protein. Cattle on pasture are often less susceptible because there is adequate energy available.
AI and ET technologies are excellent ways to improve your herd’s genetics. But without the proper nutrition, both will fail.
Dan Larson is a ruminant nutritionist at Great Plains Livestock Consulting, Inc. His experience in both cow–calf and feedlot cattle operations offers a unique perspective on the beef industry.
- Late Spring 2011