David W. Sanson
Beef cattle feed goes through a microbial fermentation process in the rumen before being digested by the animal. Since the majority of the cow’s diet is forage, efficient fermentation of this fiber is critical. Diet supplements provide additional nutrients to improve utilization of the fiber.
Mature forages – generally hay and pastures that provide less than 7 percent crude protein and are below 50 percent digestibility – are low in both energy and protein. Because of these deficiencies, it is often impossible for beef cattle to consume enough of these forages to meet requirements above maintenance. Although mature forages are low in both protein and energy, protein is generally considered the limiting nutrient for improving utilization by the rumen microbes.
Supplemental protein provides the rumen microbes with nitrogen needed to increase fiber utilization. This increases the nutrients the cow absorbs from the forage. In addition, increasing the rate of digestion allows the animal to consume more low-quality forage, giving the animal additional energy.
Supplemental protein improves the digestion of low-quality forages by 5 percent to 10 percent and improves intake by 10 percent to 20 percent. The combination of intake and digestion improvements can increase the value of low-quality forage and meet the maintenance and gestation requirements of a mature beef cow. Experimental Procedures
Ninety-six mature cows at the Rosepine Research Station near Rosepine, La., were studied in 2004, and 104 similar cows were studied in 2005 to compare the effect of supplementing cottonseed meal during the last trimester on weight change of cows consuming a mature, low-quality hay. Treatments were: no supplement, 1 pound of cottonseed meal, 2 pounds of cottonseed meal or 3 pounds of cottonseed meal. The cows were randomized into eight groups of 12 cows in 2004 and eight groups of 13 cows in 2005. Then the groups were randomly assigned to receive one of the four supplemental treatments, resulting in two replications of each treatment in each of two years.
Cow groups were maintained in 100-foot by 200-foot pens at the Rosepine Station during the supplementation period. Supplements were fed each morning, and all groups had unlimited access to a low-quality bermudagrass/bahiagrass hay.
Cows were weighed on two consecutive days before the start of the supplemental treatments in mid-October and approximately one week before the start of the calving season in mid-January. Each cow was assigned a body condition score, using a 1 to 9 scale, on each of these days. Supplementation was continued for each cow until she had calved, at which time the cow and calf were put on ryegrass pasture. Cows were also weighed and assigned body condition scores in April before the next breeding season, in June at the end of the breeding season before the study began as well as in mid-September when the calves were weaned.
Calves were born from mid-February to mid-April. At birth, calves were identified with a numbered ear tag and weighed, and male calves were castrated. Calves were also weighed each time the cows were weighed.
Cows and their calves were moved to an annual ryegrass pasture within 24 hours of calving. After the ryegrass grazing season, the pairs were maintained on bermudagrass and bahiagrass pastures until weaning. Results
Cottonseed meal supplementation increased weight gain during the last third of gestation with mature beef cows. Each additional pound of cottonseed meal improved weight gain during the supplementation period. Beef cows should gain approximately 0.9 pound of weight per day during the last one-third of gestation to account for fetal development. Weight gain for fetal development does not add any true weight to the cow and at calving this weight is lost.
Cows fed only hay lost about 90 pounds during the supplementation period; this roughly equals the amount of weight that a cow should gain to account for the increase in weight due to fetal development. Since the forage did not meet the requirement of these cows, the cows used energy stores (body condition) to provide the nutrients for fetal development. This observation is supported by condition score change during the supplementation period. Cows fed only mature hay had a decrease in body condition of 1.8 units.
Cows supplemented with 1 pound of cottonseed meal essentially maintained their weight; however, they lost more than 1 unit of body condition score. The diet of these cows was not adequate to provide the nutrients for fetal development, thus the cows used body stores to provide nutrients deficient in the diet.
Supplementing 2 pounds of cottonseed meal resulted in a weight gain during the last third of gestation of about 35 pounds. Although these cows were in a positive weight gain, the nutrient level of this diet was not adequate to provide all of the nutrients required for fetal development. These cows lost half a unit of body condition score. Cows supplemented with 3 pounds of cottonseed meal gained close to 80 pounds during the supplementation period. Thus the diet essentially met the nutrient requirements for fetal development. These cows maintained body condition during the supplementation period.
The effect of weigh loss due to calving is demonstrated in the weight change from the weight before calving to the weight taken before the breeding season. There was no difference in weight between cows supplemented with 2 or 3 pounds of cottonseed meal before the start of the breeding season; however, cows that received only 1 pound of cottonseed meal weighed less than those receiving the higher level of supplements. This difference in weight was also present at the end of the breeding season. Cows that received only hay were lighter than the other treatments at the start and at the end of the breeding season.
The level of supplementation had an effect on fall pregnancy. There was no difference between cows fed only hay and cows supplemented with 1 pound of cottonseed meal; however, both of these groups had lower fall pregnancy rates than cows supplemented with either 2 or 3 pounds of cottonseed meal. There was no difference in fall pregnancy rates between cows that received 2 or 3 pounds of cottonseed meal.
Although not significant, cows receiving no supplement had calves that were three pounds lighter at birth. At weaning, these calves were 35 pounds lighter than cows that received cottonseed meal supplementation. There was no difference in birth weight or weaning weights of calves among cows that received cottonseed meal supplementation.
Producers feeding low-quality or mature hay during the last third of gestation should provide a protein supplement. Each level of cottonseed meal supplementation improved forage utilization. Three pounds of cottonseed meal, however, improved nutrient intake enough to provide the nutrients for cow maintenance as well as for fetal development.
In the end, producers have to consider the relative condition of their cows during pregnancy, the cost of supplemental feeding and the quality of the forage the cows will receive following calving. The value of supplemental feeding is most reflected in the success of breeding the cows for the next season, and the data show that cows that lost the most weight during this study had a much lower pregnancy rate the following season. David W. Sanson
, Associate Professor, Dean Lee Research Station
, Alexandria, La.(This article was published in the summer 2007 issue of Louisiana Agriculture.)