From the June issue of Cow/Calf Producer.

For some, the breeding season may be over; for others, it is still ongoing. Regardless when the AI guns get put away and the bulls are taken out of the pasture, we must assess how well the breeding season went. The results reflect how good of a job we did meeting the nutritional needs of the cow herd. Cow herd nutrition is a year-round concern that can’t always be relegated to minimal-input supplement choices in the fall and winter. Rather, there should be an ongoing assessment of the balance of cow requirements and nutrient supplies.

The body-condition score (BCS) — the assessment of the fat cover the cow is carrying — of a cow and the herd overall is the best indicator of past nutritional status or success of the overall nutritional program as well as near-term nutritional needs. Surplus nutrition (energy) causes fat to be deposited, whereas an energy deficit causes fat to be mobilized. The amount of fat has an influence on the hormones and physiology of the cow. If you are not familiar with body-condition scoring your cow herd, you should be, so contact your local county Extension agent. It is the least expensive, but greatest return, management technique a cattle producer can adopt. Unlike other management techniques, body-condition scoring is free, can save feed resources and dollars, and can increase returns to the cow-herd enterprise.

The attention to cow herd year-round nutritional needs arises for two primary issues. First is the relationship of nutritional status, BCS and cow herd reproductive productivity. The BCS of the cow herd has a lot to do with reproduction, and reproduction has everything to do with profitability. Studies have examined the effect of cow BCS on any number of reproductive and productive traits. Summarizing data from three citations (DeRouen et al., 1994; Spitzer et al., 1995; Vargas et al., 1999) that cover a range of BCS and locations provides a nice data set to apply some simple economics to the cost of cow BCS. Table 1 presents my interpretation of the economic impact that cow BCS (3 to 5) has on productive outcomes. Because low BCS cows have decreased pregnancy rates, wean fewer calves, wean lighter calves, and return less overall dollars to the herd, the impact of BCS on cow herd profitability is considerable.

The second area is the concept of cow nutrition during gestation impacting offspring performance — referred to as fetal imprinting or fetal programming. The developing fetus is completely dependent upon the dam for its nutrient supply from conception until sometime before weaning. As a result, any nutritional insult to the cow may likely result in a nutritional insult to the developing fetus. Throughout gestation there are critical time points of development for the fetus. Critical shortages of key nutrients including protein/amino acids, fats, vitamins and minerals, and low cow energy supply can result in sub-optimal development in the growing fetus. We know that decreased energy supply to the cow can affect placental development, fetal development, calf birthweight and, ultimately, reproductive performance. Likewise, once the calf is born, if its dam was nutrient-restricted during gestation, sickness and death rates increase in those calves. Recent work in cows has identified protein supplementation and higher-quality forages as important contributors to improved reproductive performance in heifer offspring through decreased age at puberty, increased pregnancy rate and increased proportion of heifers that calved in the first 21 days of the calving season. Steer progeny had greater weaning weight, feedlot average daily gain and carcass weights, and better carcass quality.

Often our cow herds experience a period(s) of nutritional restriction during the annual production cycle. Nutritional restriction of the cow not only affects her ability to maintain herself but also her ability to become pregnant and maintain pregnancy, and can negatively affect the developing calf. Early nutritional restriction of the cow can affect the placental development and the cow’s ability to deliver nutrients to the fetus. Late nutritional restriction of the cow negatively affects the development of organs and uptake of nutrients by key tissues. The opportunity to negatively or positively affect a calf crop and the economic return from the calf crop ultimately starts with cow nutrition.

Table 1. Impact of cow body-condition score (BCS) on performance measures and economic outcomes

Outcome measure

BCS 3

BCS 4

BCS 5

Pregnant %

70

75

80

Weaning %

38

73

77

205-d weight, lbs.

411

439

444

Weaning weight, lbs./cow exposed

158

322

342

Economic impact1

 

 

 

Pregnant %

$88,200

$94,500

$100,800

Weaning %

$33,868

$69,363

$77,616

205-d weight

$468

$487

$491

Weaning weight, $/cow exposed

$379

$773

$821

1Assumptions: 100 cows in the herd, all calves are marketed, weaning weight = 525 lbs., market price of $240/cwt.