Last month, my column focused on meeting the nutritional needs of late gestation cows. This period is one of the most important periods in the reproductive calendar of the cow, as it is a time where 70 per cent of fetal growth occurs. This month, I want to focus on the nutritional needs of the lactating beef cow, particularly that time frame from calving through breeding. In order to do this, I want to go through a checklist of nutritional needs that should be addressed, if we are going to assist that cow in raising a healthy calf and successfully rebreed.
First let’s review a bit of postpartum physiology using a 1,400-pound freshly calved beef cow in good condition as our example. Without a doubt, her first post-partum challenge is lactation, initially colostrum followed by milk. From a nutrient requirement perspective, lactation places a large demand on the cow’s body. Requirements for energy and nutrients such as protein, calcium and vitamin A increase significantly over that required during the last trimester of pregnancy. Failure to meet these needs will result in loss of body condition as the cow strives to produce milk for the calf. Further compounding matters, lack of energy or key nutrients such as protein can drop the amount of milk produced, thus negatively influencing calf growth.
Concurrently, the cow’s body starts to recover from the stress of pregnancy and calving. Most importantly, the uterus returns to its normal shape and size and the hormonal milieu responsible for the estrus cycle is reactivated. This recovery process normally takes up to 40 days to complete. It is important to note that the cow is infertile during this period and thus minimizing its length is critical if she is to maintain a yearly calving interval. As with milk production, the length of the post-partum anestrus period is largely tied to body condition and nutrition status. Loss of condition following calving will cause a delay in return to breeding status and potentially a reduction in first service conception rates. Simply put, cows in poor condition post-calving and/or deficient in one or more key nutrients will take longer to re-breed, if they re-breed at all.
So, from a nutrition perspective, what are the steps you can take to make sure your cows are ready when the breeding season starts? First let’s consider the energy requirement of our example cow using Alberta Agriculture “Cowbytes” program. Let’s assume she is consuming two per cent of her body weight as dry matter (DM), is not cold stressed and is of aver- age milking ability. In her last month of pregnancy, her total digestible nutrient (TDN) requirement was approximately 15.5 lbs. per day, a requirement met by a diet with a TDN concentration of 56.0 per cent (DM basis). As we saw last month, this requirement can be met by feeding appropriate quantities of good-quality hay, properly preserved cereal silages or poorer-quality forages supplemented with an energy source (i.e. cereal grains).
Two months post-calving, however, her TDN requirement has jumped to 18 lbs. or an increase of 16 per cent. To compensate for this increase, the cow’s appetite will naturally increase. However, in order to minimize loss of body condition, dietary energy concentration will also need to increase. For example, if DM intake of our cow increased post-calving to 2.2 per cent of body weight, dietary TDN concentration would need to increase to 63 per cent (DM basis) to meet the increased TDN requirement. With the exception of good-quality alfalfa hay and cereal silages, most of our conserved forages will need some form of energy supplementation to achieve this concentration of TDN.
As with energy, protein requirements increase significantly after calving with peak production occurring approximately 40 to 50 days post-calving. While there is variation in the milking ability of individual beef cows, it is normal to see post-calving diets formulated to 10 to 11 per cent crude protein. Forages such as good-quality grass and/or alfalfa hay, legume silages and some cereal silages can go a long way to meeting this need. However, a protein supplement will be necessary with corn-silage based programs or when feeding poorer-quality forages, particularly cereal crop residues.
Finally, it is also important to pay close attention to the mineral/vitamin nutrition of the post-calving cow. Lactation increases the demand for macro minerals such as calcium, phosphorus and magnesium. Failure to supplement these minerals in a balanced ration can cause issues with milk fever and/or winter tetany as well as influence post-calving conception rates. Similarly, trace mineral deficiencies (i.e. copper, manganese, zinc, selenium) can negatively influence the cow’s health and reproductive success. Such deficiencies can be real, such as a lack of dietary copper, or induced due to dietary mineral imbalances such as too high a level of dietary sulfur or molybdenum. From a vitamin perspective, lactation dramatically increases (i.e. as much as 40 per cent) the vitamin A requirement of the post-partum cow. While it is possible to inject vitamins A, D and E, ensuring adequate dietary intake through a mineral or supplement program is the most cost-effective method of meeting this requirement.
To close, the goal is a balanced nutrition program that meets the requirements of the post-partum beef cow for lactation and re-breeding. Checking off the above “boxes” can help you ensure that your cows meet both objectives.