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Nutritional Management: A Tale of Two Seasons

Posted Nov. 1, 2000

The NF Ag News and Views newsletter exists to furnish information that is both timely and useful. One of the predominant questions that I have been asked pertains to calving season management; more specifically, should one employ a defined calving season or calve year-round? A controlled calving season means bulls are with the cows for a defined period, usually sixty to ninety days. A major hindrance in implementing this type of season is that, unless you have multiple herds calving at different times, bulls have to be kept away from the cow herd for a large portion of the year. Other disadvantages include marketing cows that did not breed during the controlled season and maintaining optimum stocking rates once unbred cows are culled. Conversely, advantages of controlling your calving interval include less stress on both you and your animals; less time and labor; calf uniformity, which could lead to more marketing venues; and specific calving periods, namely, not during planting, plowing, or vacation. Another notable advantage to scheduled calving is the ability to supplement according to more uniform cow requirements.

This summer, most of southern Oklahoma and northern Texas experienced the worst drought in almost twenty years. Producers began asking when and with what to supplement cows in various stages of production. In order to adequately answer this question, we must know a few things. To provide a supplementation program that is both cost effective and nutritionally balanced, forage quality and animals' nutritional requirements must be determined.

The National Research Council estimates that lactation increases energy demands by an average of 20 percent. Therefore, cows scheduled to calve within a specific interval have uniform requirements and can receive supplements accordingly. Table 1 represents crude protein (CP), total digestible nutrient (TDN), and dry matter intake (DMI) requirements for cows of various weight classes and milking ability during peak milk production and three stages of gestation. As is expected, nutrient requirements and feed consumption are highest during the first ninety days of lactation but lowest during the second trimester of gestation because milk production declines and the fetus grows very little. Therefore, for spring-calving herds (March through May), nutrient requirements would be lowest during early fall, and fall-calving cows (August through October) would have lower supplemental demands during late winter and early spring. For operations calving year-round, supplementation becomes more of an on-average approach that leads to over- or underfeeding portions of the herd, which in turn means more input costs.

Estimating forage quality and quantity can be difficult; however, this information is needed to ensure that feeding practices include nutrients provided from the forage base and that dry matter intake is predicted correctly. Numerous reports indicate that cattle are somewhat selective in their eating habits and thus can consume a diet that is more nutritious than one that you or I could hand clip. Nevertheless, laboratory analysis of a hand-clipped sample is better than nothing at all and is more objective than visual appraisal or historical estimates.

Table 2 represents possible nutrient deficiencies for cows of average and high milking ability that are grazing dormant winter pasture during four physiological stages of production. Let's refer to the spring and fall calving situation mentioned earlier. Spring-calving herds would be in the second trimester of gestation and, depending upon body condition, very little or no supplementation would be needed. However, if fall calving were employed, then cows would be approaching the end of peak milk yield and starting on the first trimester of gestation. Consequently, neither CP nor TDN under these forage conditions could meet requirements, and supplementation (feed, hay, or winter pasture) would be in order.

Deciding to implement a controlled calving season is up to the producer and must be warranted economically and managerially. However, considering that supplemental feeding composes a large portion of a ranch's input cost and that a cow's nutrient requirement varies, one advantage to a controlled calving season is more uniform nutrient requirements of the cow herd and less need for supplementation.