Farming Magazine - December, 2011

COLUMNS

Dairy Nutrition: Time Is No Friend for a Dairy Cow

By John S. Hibma

One of the most critical management areas on the dairy farm is that of reproduction. In order for a cow to produce milk, she has to first produce a calf and then continue producing calves about every year or so. On the modern commercial dairy farm, getting cows pregnant again 60 to 90 days after giving birth will have a significant impact on the profitability of the dairy farm, because it ultimately reflects on how many fresh cows there are in the herd at any given time. The longer a cow remains open (not pregnant) the greater her chances become in being removed from the herd for decreased milk production in the future.

Dairy cows are under a lot of pressure to do a lot of things in a short period of time.

Nutrition has an important impact on the reproductive performance of dairy cows, and diet-ary energy is the major nutrient required for them to conceive. The metabolic event that we call Negative Energy Balance (NEB) is a condition that nearly all cows experience at the time of calving and into the beginning of the lactation. It's caused by not enough dietary calories being consumed through her diet for the amount of milk she's producing. Often at the beginning of the lactation a cow will metabolize her own body fat and muscle to compensate for the lack of nutrients in the diet. However, this condition will not last indefinitely, and the cow will eventually begin limiting milk production in favor of keeping her own body from devouring itself. At the same time, reproduction functions are delayed.

A negative energy balance affects a cow's reproduction performance. Ovulation and the onset of showing estrus are both affected when a cow is in NEB. Essentially the production of hormones, the development of follicles, the release of eggs and the establishment of early pregnancy all require energy coming from the diet. When that energy is not there, the cow's system will recognize that, and consequently she will not show heat or conceive.

In many ways the dairy industry has caused and exacerbated the problem of poor reproduction performance in dairy herds. The pursuit of higher-producing cows has had a negative impact on their ability to conceive quickly in the next lactation. In many ways, the industry has fallen behind the curve in feeding the high-producing cow during those days before calving and the weeks after. Along with that, there are increased risk factors associated with NEB, including uterine infections associated with retained placentas and milk fever. A severe case of NEB bodes poorly for a cow's ability to become pregnant early into her next lactation.

We have several nutritional strategies available to improve reproductive success in dairy cows after they've calved. The single most important driver for minimizing NEB is to maximize dry matter intakes (DMI) during the transition period. Cows generally stop eating a day or two before they calve. So, providing a diet during the last couple of weeks before they calve that provides plenty of nutrition and keeps the rumen stimulated will go a long way towards avoiding both metabolic and hormonal problems after calving.

Nearly all cows, first-calf heifers and older cows alike, can benefit from a diet with higher energy density at the time of calving. This means more calories per pound of feed consumed. The addition of a rumen-protected fat as well as several pounds of a starch source is pretty much a necessity all year long for dairy diets in the Northeast U.S. This is often a source of debate, however, during these tough economic times when feed prices are climbing and dairy farmers are looking for ways to reduce costs. Transition and close-up diets containing 2 to 3 more megacalories per pound (mcal/lb) will dramatically reduce NEB and loss of body condition during early lactation.

Monitoring of transition and fresh cow body condition will also aid in getting cows bred on time. Body condition scoring essentially tells us if a cow is too fat or too skinny relative to her stage of lactation and level of milk production. The system for milk cows uses a scoring procedure of 1 to 5, with 1 being extremely thin and 5 being extremely obese. Keeping track of a cow's body condition score (BCS) at several stages of lactation enables us to better manage her nutritional needs during the lactation and dry period. One BCS increment represents about 120 pounds of weight on a Holstein and about 80 pounds on a Jersey. Drastic weight loss during early lactation indicates a severe NEB and should be avoided. Along with that, cows freshening too thin is also an indication of inadequate dietary energy during the dry period, and this will also impact their ability to ovulate and conceive a pregnancy. Generally, the first ovulation after freshening occurs 10 to 14 days after energy balance has begun returning to a positive status. Severe weight and BCS losses caused by inadequate feeding or illnesses will often result in cows that show no heat or develop cysts on their ovaries. In fact, cows still having low BCS at 65 days after freshening are likely to not show heats and have cysts.

Our dairy cows are really under a lot of stress to make milk and get pregnant every year, but they can't be expected to do each of these when their diets are inadequate. There are many interrelated factors that all contribute to poor conception rates in dairy herds, chief of which involves keeping a high-quality ration available to dry cows throughout the day. Many metabolic problems can be completely avoided simply by making sure cows have a balanced diet of energy, protein, vitamins and minerals.

An extended lactation due to poor reproduction performance is ultimately a "death card" for a cow and a huge loss in profits for the dairy farm. Poor reproduction performance on dairy farms is one of those areas that are nearly totally within the control of the dairy farmer and his management team. Formulating rations that keep energy status elevated for fresh cows is the foundation to getting cows pregnant and keeping them making money for a long time to come.

The author is a dairy nutritional consultant and works for Central Connecticut Farmer's Cooperative in Manchester, Conn.