The Cow-Calf Manager
Livestock Update, June 2001
John Hall, Extension Animal Scientist, Beef, VA Tech
The drought this spring was shaping up to be a wicked one until the recent rains. Still, many Virginia farms have not received appreciable rainfall. Pastures and hay fields are in the worst shape of any recent spring. As a result, cows are losing weight and they may suffer reproductive problems.
Cows must cycle early in the breeding season in order to calve on time next year. For years, research has indicated that cows that calve in good body condition (BCS 5, 6 or 7) are more likely to cycle early and breed back during a controlled breeding season than are thin cows. In addition, several studies have demonstrated that once cows resume cycling after calving, they must lose a tremendous amount of weight to stop cycling. Cycling cows have to become a body condition score 2 or 3 before they will quit having reproductive cycles. This means an average cow would need to lose 300 or more pound before they will stop cycling.
Based on this information, we always felt that if we could get a beef cow cycling after calving we could usually get her bred. The same appeared to be true for virgin heifers. However, several studies indicate that severe weight loss before or during the breeding season can result in decreased pregnancy rate even though cows are cycling. One study in Montana developed heifers on high, medium and low energy diets. Even though 80 % of the low energy heifers cycled during the breeding season only 50% of them became pregnant. In the high and medium energy groups, pregnancy rates were 82% to 85%. The researchers concluded that there was an increase in early embryonic mortality resulting in lower pregnancy rates.
More recent research indicates that poor nutrition after cows are cycling, but before conception, may result in a variety of problems that may impair reproduction. Poor nutrition during the breeding season has been linked to a poor uterine environment. As a result, fertilized ova (eggs) do not implant and grow. Another problem appears to be altered follicular development so the ova do not develop properly or are not released at the right time for high rates of fertilization. All these factors work against cows getting pregnant.
In most years when pasture is plentiful, mature cows that calve in good body condition only need a good free choice mineral mix containing high selenium trace mineral salt with some calcium and phosphorus (i.e. complete mineral). However, when cows are thin at calving or pasture is limited between calving and breeding, cows will need supplemental energy. Five to eight pounds of corn or good free choice quality hay may be fed to provide the additional energy. Cows will not need a protein supplement as long as some pasture is available to graze. Spring and early summer pasture is high in protein, usually over 20% crude protein, so it acts as a protein supplement to the other feeds.
First and second calf heifers have higher nutritional requirements. First and second calf heifers are still growing as well as lactating during the breeding season. These heifers will need about the same total amount of energy as a mature cow, but they eat about 15-20% less feed. So these young cows need 4 to 5 lbs. of corn, corn gluten or barley daily in addition to all the high quality pasture than can eat. This will meet their extra energy needs and help them breed back quickly.
However, when pastures are short or poor in quality young cows will need up to 1% of their body weight in corn, barley or corn gluten. This means about 10 lbs. of supplement per heifer per day. This may sound like a lot of feed, but when pasture is short or low quality, we must supply the extra nutrition by feeding.
Our spring calving herds are at a very critical time. Either we pay for extra feed now, if needed, or we will pay for it in open cows this fall and fewer calves next spring.