Data suggest that dormant winter native range is deficient in protein for spring-calving cows. Previous data at many Land Grant Universities and the University of Nebraska suggest that protein supplementation of spring- calving beef cows grazing dormant Sandhills range during late gestation does not improve cow reproductive performance (2006 Nebraska Beef Report, pp. 7-9), namely pregnancy rate, despite the fact that nutrient requirements are greater than nutrient content of the grazed forage. In a more recent study (2009 Nebraska Beef Report, pp. 5), spring-calving cows (3 to 5 years of age) were either supplemented a pound of a 28% crude protein cube daily or not supplemented protein while grazing dormant native range and their performance was evaluated. After winter grazing, supplemented and non-supplemented cows were managed together. Cow body weight and cow body condition pre-calving was greater for cows that were supplemented. Those difference were not seen prior to the start of the breeding season nor at weaning. Pregnancy rate was not different between the supplemented and non-supplemented groups and were above 92%. Calf birth weight was not different between the two groups. However, calves from supplemented dams were heavier at an interim weigh date in the spring (before the start of the breeding season for the cows) and at weaning despite the fact that there was no difference in milk production of dams that were either supplemented or not supplemented prior to calving. This might suggest that calves from dams that were supplemented precalving may be more thrifty and their immune system status was better able to word off sickness; therefore better gains. However, there was no indication of any differences in calf sickness between calves from dam supplementation or non-supplemented groups. It might also suggest that calves from dams that were supplemented are more efficient at using feeds. Another suggestion might be, although milk production was not different, it might suggest that there are milk quality differences or possibly the quality of the colostrum differed in supplemented compared to non-supplemented dams. As interesting, statically more cows that were supplemented (83%) while grazing dormant native range precalving calved the first 21 days of the calving season compared to non-supplemented (62%). Cows that calve early in the calving season wean calves that are heavier and should generate more dollars at weaning.

In the same study reported above, a similar group of spring-calving cows were supplemented the same protein cube while grazing corn stalk residue and there was a group of cows grazing corn stalk resides that was not supplemented. After corn stalk grazing, cows were managed together. Pre-calving weight and body condition were statistically different between the two groups in favor of the supplemented group of cows. In the corn stalk grazing part of the study, the difference between the supplemented and non-supplemented groups was not the same magnitude as that observed in the cows grazing dormant native range. Precalving body condition score for cows grazing corn stalks and supplemented was 5.3 and that for non-supplemented cows was 5.2, although these numbers are statically different, they are likely not different biologically, meaning it would be difficult to say that any performance difference between the two groups is a result of differences in body condition; nor would you expect any differences in performance due to differences in body condition of the two groups. There was no difference in calf birth or weaning weight. Calving date, percentage of the cows calving the first 21 days of the calving season or milk production was not different. Pregnancy rate was high for both groups (97% for supplemented and 95% for non-supplemented cows).

The fetal programming hypothesis states postnatal growth and physiology can be influenced by stimulus experienced in utero. Can the performance of calves be influenced by nutrition of the dam during late gestation? The study described above evaluated steer and heifer performance from supplemented and non-supplemented dams that were either grazing dormant range or corn stalk residue. Heifers from dams that grazed corn residue tended to weigh more pre-breeding compared to heifers from dams that grazed native range whether they were supplemented or not. Heifers from dams that were supplemented while grazing range or crop residue were younger when they reached puberty. Pregnancy rate tended to be greater for heifers from dams that were supplemented protein precalving compared to heifers whom dams were not supplemented. The differences in reproductive performance for heifers was more pronounced if their dams grazed native range compared to corn stalks. Pregnancy rate for heifers from dams that were supplemented and grazed range was 90% compared to 77% for heifers whom dams were not supplemented. Pregnancy rates for heifers from dams that were grazing corn stalks and supplemented was 88% compared to 83% for heifers whom dams were not supplemented.

The performance of the steer mates to the heifers discussed above was also recorded. Carcass weight tended to be greater for steers from supplemented dams compared to steers from non-supplemented dams. Backfat, ribeye area, and yield grade were not different between steers whom dams were supplemented compared to steers whom dams were not supplemented. Percentage of the steers grading USDA Low Choice or better was greater for steers from dams that were supplemented compared to steers from dams that were not supplemented. The greatest difference in percentage USDA Low Choice was in steers from dams that grazed corn residue and were supplemented (86%) compared to steers from dams that grazed corn residue and were non-supplemented (64%).

Source: Dr. Rick Rasby, Professor of Animal Science, Animal Science, University of Nebraska - Lincoln