Excerpt by: C.P. Mathis, Extension Livestock Specialist, Range Improvement Task Force
J.E. Sawyer, Extension Livestock Specialist
In the Southwest, pasture forage (that is, payment on purchased or leased land) is generally one of the largest fixed costs. So it is important to match cow type to the forage supply to achieve maximum efficiency in harvesting the forage and converting it to a cash commodity-the calf. Many factors can affect production efficiency in the cow herd. Major factors include cow size, milking ability, and reproductive performance. The purpose of this guide is to address the relationship between these factors and beef production efficiency in the Southwest.
Energy intake comprises a large portion of the input into the cow herd. Maintenance energy (the amount of energy required to maintain body weight) can represent 70 to 75 percent of the total energy consumed annually by the cow herd (Ferrell and Jenkins 1985). A cow’s size or body weight does not influence her energy use efficiency (Ferrell and Jenkins 1984a, 1984b). However, researchers from Wisconsin (Davis et al. 1983b) have shown that smaller cows can wean more pounds of calf per pound of feed than can larger cows. The same research group (Davis et al. 1983a) in a different study found that feeding larger cows a higher-energy diet did not increase enough the number and total weight of calves weaned to offset the higher level of energy intake. In other words, supplying larger cows with more energy did not increase their production efficiency.
So a larger cow can produce a larger calf, but her production efficiency may be suboptimal. In general, cows can be selected for improved efficiency in a certain environment, but they may not be as efficient in other environments (Ferrell and Jenkins 1985). In an environment where feed resources are unlimited, larger cows may be able to offset the inefficiency by weaning larger calves. Generally, however, on Southwestern rangelands where forage supply often is limited, larger cows are not as efficient as smaller cows.
Cow Milk Yield
Milk yield is related to preweaning calf growth (Clutter and Nielsen 1987), so increased milk yield often is considered an advantage in a cow-calf operation. But milk production requires high levels of energy input by the cow, and, if feed resources are limited, milk production can have a negative effect on the overall efficiency of beef production.
Researchers from the Meat Animal Research Center in Nebraska (Ferrell and Jenkins 1984a, 1984b, 1985) have shown that energy use is less efficient in higher-milking cows. They attribute their observations, in part, to the higher-milking cows’ larger internal organs and faster metabolism compared with lower-milking cows. The low energy use efficiency of higher-milking cows means that they require more energy per pound of body weight than do lower-milking cows.
Therefore, a higher-milking cow generally has a greater total energy requirement than a lower-milking cow of similar size during the lactation and dry periods (Ferrell and Jenkins 1984a; Montano-Bermudez et al. 1990).
Scientists at the University of Nebraska (Montano-Bermudez et al. 1990) have estimated maintenance requirements for cows with low, moderate, and high levels of milk production during gestation and lactation. Requirements were calculated per unit of body weight, with Hereford X Angus (lowest milking potential) having the lowest requirements, and the moderate- and high-milking females having similar but higher requirements.When calculated for cows of equal body weight, the maintenance requirement for lower-milking cows compared with highermilking cows was 0.8 pounds less total digestible nutrients (TDN; an estimate of energy intake by the animal) per day during gestation (6.4 vs. 7.2 pounds TDN) and 0.9 pounds less TDN per day during lactation (8.3 vs. 9.2 pounds TDN). When considered across a production cycle so that energy use for gestation and lactation were both included in the estimates of energy requirements, differences were much larger (Montano-Bermudez et al. 1990).