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Correlation of Nutrition and Breeding by Dr. David Porter Price, Nutritionist We see a lot of discussion about vibriosis, trichomoniasis and a number of other diseases that can affect reproduction. Likewise we hear a lot of talk about copper and various other trace minerals that likewise can affect reproduction. Certainly this information is important, but there is so much emphasis on these highly specific problems, that many producers and veterinarians overlook the obvious. That is, 90 percent of the breeding failures are not due to disease or a lack of individual nutrients, but a simple lack of energy. In the vast majority of cases it's a function of how many groceries the cows did or did not get. Body Condition Score. To approach this problem of energy, the universities and most extension services have focused on the condition of the cow. The bottom line is that while on average a cow in good flesh is more likely to conceive than a thin cow, through knowledgeable supplementation the conception rate of thin cows can be nearly, if not equally as good. This does not mean it should be made a practice to let cows become thin; but if faced with that situation, a little understanding of nutritional physiology can save the day. What we are going to discuss was proven on a practical basis nearly 40 years ago. The scientific basis for it, I predict will be proven within the next two or three years. Currently, the scientific analysis has been primarily focused on humans. Specifically, the talk of human nutrition the last few years has been the discovery that fat cells secrete a hormone. Known as leptin, in humans this hormone is known to have a strong influence on the hunger sensation. In swine, it has been proven to trigger estrus. Clearly it is only a matter of time until it is shown that leptin is also involved in triggering estrus in cattle. In the late 1960's Dr. John Wiltbank reported that for cows to ovulate they had to be "in a positive energy balance." In other words, they had to be gaining weight. Dr. Wiltbank found that you could take thin cows, put them on a high energy ration, and shortly thereafter they would begin cycling. Using measured levels of feeding, Dr. Wiltbank found that the average dry beef cow needs at least 8.0 lbs. of TDN (total digestable nutrients) in order to begin cycling. What was curious was that it was almost a "threshold" event. At 7 or even 7.5 lbs. of TDN; conception rates would be in the 40's, or even lower. Break over 8.0 lbs., and 90 percent would be cycling. When fat cells are growing they secrete this hormone. It seems highly likely that the presence of leptin in the blood stream is what triggers estrus. As a practical matter, of course, it doesn't matter. The take home message is that if cows are not cycling; take a look at your forage. Drought. If you are in one of the western states experiencing drought and your grass is dry and mature, then you will probably need to supplement. If you are not in a drought, but your forage is not particularly lush and your cows are thin, then you will likewise probably need to supplement. What to Supplement. Under drought conditions, you will need to supplement both energy and protein. As you'll remember from Ruminant Nutrition 101, protein is required not only for the animal, but for the rumen microorganisms as well. On dry, mature grass there is usually inadequate protein to allow a maximum rumen microbial population. This reduces fiber digestion; thereby reducing the amount of grass the cow can eat. Add some protein, and this increases the amount of forage the cows can eat. For dry cows, often protein supplementation alone is enough to increase TDN intake to start them cycling. For cows nursing calves, it will take more. The actual amount will depend upon milk production, however, somewhere in the neighborhood of 12 lbs. of TDN is good. As a practical matter, if the grass is dry and mature, it will take supplemental energy, in addition to protein, to get cows cycling. How much supplement. If the calves have been early weaned, in many cases a pound or so of a good quality protein supplement such as cottonseed or soybean meal is all it will take. That is, on dry mature grass adequate protein can increase overall grass consumption by 30 or even 40%. This increased intake can often be enough to bring total TDN to a level to allow cows to cycle. If the calves have not been weaned, then usually it will take from three to about five pounds of grain or other energy concentrate; in addition to protein. With respect to protein, remember that lactating cows require nearly twice as much as the dry cows. The Bottom Line. Supplementation during the breeding period can allow thin cows to conceive similar to cows in good flesh. But even if cows are in good flesh, drought dormant grass can limit conception. Under drought conditions, even cows in good flesh can benefit from supplementation. |
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