Post-breeding Management and Heifer Pregnancy Rates
By Scott Lake, UW Extension Livestock Specialist
The yearling heifer represents the best genetics and serves as the future of the cowherd, and heifers need to reach puberty and start cycling prior to the breeding season, for best results.
It is well documented that heifers need to reach a target body weight (at least 650 pounds for British breeds and 750 pounds for Continental breeds) to attain puberty prior to the breeding season. Assuming that a heifer has reached puberty, recent research has suggested that a larger percentage of heifers conceive to their first service (AI or bull bred) than originally thought. However, sometime between conception, when the heifer’s body recognizes that she’s pregnant (~14 days post-breeding), or when that fetus attaches to the uterus (~30 days post-breeding), the pregnancy is sometimes terminated.
There are numerous factors that could lead to a heifer not maintaining a pregnancy, and frequently the most overlooked aspect is nutrition.
Beef producers spend a lot of time, effort and money getting heifers to the proper weight and body condition prior to breeding, and the same can be said for either artificially inseminating (AI) heifers or researching and buying heifer bulls. However, it often appears that once AI is completed or the bulls are turned in, that nutritional management is over and the heifers are simply turned out on pasture.
There is a common belief that spring grass is about the best feed available, and this is partially true. There’s no doubt that spring grass is high quality, but the real question is what plane of nutrition were these heifers fed until breeding? Heifers that are fed a high energy (corn silage, corn, etc.) diet in a dry lot from weaning until breeding and then turned out onto pasture after breeding suffer a dramatic decline in dietary energy density, even in quality pastures. It may take a couple weeks for these heifers to adapt to their new diet, and the change may be subtle, with very little drop in condition score, but this decrease in plane of nutrition coincides with maternal recognition of pregnancy and may result in embryonic loss.
Recently we tried to answer some of these questions with a nutritional study at UW. For this study, heifers were fed a ration designed to gain about 1.5 pounds/day prior to breeding. Immediately after breeding, one group of heifers were maintained on the same diet for 20 days, another group of heifers were fed a diet designed to maintain (neither gain or lose) body weight for 20 days, and the last group was fed 80 percent of their maintenance requirements for 20 days. After 20 days, all heifers were fed a similar diet.
A pregnancy check utilizing ultrasound technology at 35 days post-breeding revealed a 15 percent increase in pregnancy for the group of heifers maintained on the 1.5 pounds/day gain through breeding. There was no difference between the other two groups. This study was designed to mimic the effects that a heifer could potentially go through when they are fed a dry lot diet and then placed on pasture.
On the other end of the spectrum, excess protein can cause changes in uterine environment and lead to embryonic loss, as well. Caution should be taken with feeds high in protein (distillers grains, certain spring pastures, etc.). Our recommendation is to keep heifers on the same plane of nutrition for about a month after breeding. If heifers are raised on a high energy feed in a dry lot, the best situation is to keep them in the lot an additional 30 to 45 days on the same feed.
The obvious problem with this scenario is getting them with the bull, however, a plausible solution may be to turn bulls into the dry lot. This scenario would keep heifers in close proximity to the bull for easy breeding and allow for a shorter breeding season. In this situation, the heifers can be shipped to pasture already bred. Most commercial heifer development lots will work with producers on this type of program, and the additional feed costs incurred in the dry lot would be more than made up for with the increased percentage of heifers maintaining their first service pregnancy.
For heifers developed at home or on a range-based system, it is recommended that they be acclimated to pastures prior to breeding (~30 days). Supplements may be needed to maintain dietary energy; however, with a lower energy forage based diet, spring pasture will often provide an increase in dietary energy density. Regardless, if the change in nutritional plane can take place prior to breeding, more of those heifers will maintain their pregnancy.
Another important factor in maintaining pregnancy is stress. As mentioned previously, there are key biological events during pregnancy that may affect the success of the pregnancy. One of these critical windows of metabolic activity is between maternal recognition of pregnancy (14 to 17 days after fertilization) and implantation of the embryo (~42 days after fertilization). Dramatic changes in diet and transportation of cattle long distances during this period may result in early embryonic loss. For those producers who AI their heifers, the general recommendation is that heifers should be moved or transported within eight days after AI (excluding the first 24 hours post-AI), or 40 days after insemination.
There are varying philosophies regarding how heifers should be developed. One approach is to feed them high-energy feedstuffs to maximize the number of heifers that attain puberty and conceive, while the contrasting approach is to rough them through on a low energy diet and select from those that develop and conceive. Regardless of individual philosophy, these heifers represent a significant investment of both time and money, and represent the future of the cowherd. If we have invested the time and money to retain and develop her, regardless of system, doesn’t it make sense to give her every opportunity to not only breed, but to also maintain that pregnancy?
By reducing her stress, both nutritional and physiological, during the key metabolic periods discussed above, we can help maximize the number of pregnancies maintained.