Protein vs. Energy?
John Paterson, Professor of Animal Science
Montana State University
The cost of energy supplements can be less than that for protein supplements. Which one is better for the productivity of replacement heifers grazing on native range? This past summer with the above average rainfall in Montana, we have seen forage samples that are low in both protein and total digestible nutrients (TDN). Work from Oregon showed that protein content of native range was higher during years when rainfall was below normal compared to years when rainfall was above normal. This observation suggests that producers need to pay careful attention to meeting the nutrient requirements of cows and especially replacement heifers by investing in a forage analysis. Dr. Joe Wallace a well respected range nutritionist from New Mexico State University conducted experiments with yearling range heifers to compare the response when supplemented with either a 41% protein supplement vs. a 9% protein-energy supplement. In addition, he wanted to determine how gains and pregnancy rates were affected if he fed the supplements once a week or two to three times per week. He did this knowing that supplementation costs include labor and vehicle costs in distributing the supplements. The first experiment compared performance of yearling heifers (average initial weight of 470 lbs) fed a cottonseed cake supplement three times per week vs. heifers fed the same supplement once per week. Heifers supplemented three times per week were fed on Monday, Wednesday and Friday, while those fed once weekly were fed on Tuesday. This experiment was conducted over two years and in the first year heifers received 7 lbs of cottonseed cake once weekly vs. 2.3 lbs of cottonseed cake three times/week. In the second year, heifers received 10 lbs of cake once a week vs. 3.5 lbs of cake three times per week. The results of these two trials are presented in the following table.
Growth rates were not affected by supplementing heifers once a week vs. three times per week. Fall pregnancy rates did not differ between treatments. The reason that there were lower pregnancy rates in the second year was because many of the heifers had not reached puberty when the trial was conducted. The major finding of this research was that once a week supplementation reduced transportation and labor costs by 60%. The second study was conducted to compare yearling heifer response when fed one of three supplement treatments: 1) cottonseed meal cake fed twice a week at 7 lbs/feeding; 2) a grain cube containing 9% protein fed twice a week at 6.4 lbs/feeding and 3) the same grain cube fed daily at 1.9 lbs/head/day. The results of this 156 day experiment are presented in the following table.
Total gains were much better for heifers fed the protein supplement twice weekly (80 lbs of gain) compared to heifers fed the 9% protein grain-cube twice weekly (lost 59 lbs) or fed the cube daily (gained 22 lbs). The most interesting results were that source of supplement had a dramatic effect on first service conception rates. While all the heifers fed protein supplement conceived during the first 21 days, only 59% of the heifers fed grain cube twice weekly conceived during the first 21 days. The heifers which were fed grain daily were intermediate (81%). Overall pregnancy rates for heifers fed protein or energy supplements twice weekly were not different, but were significantly higher than heifers fed the grain supplement twice weekly. Summary. The results of these two experiments showed that reproduction of heifers fed protein once per week were similar to heifers fed protein three times a week. However, when fed a grain cube twice weekly, first service and overall pregnancy rates were poorer that feeding the grain cake daily. First service conception rates favored (significant difference; P<0.05) protein supplementation (41% protein) rather than grain cake (9% protein).
Questions? Give John a call at 406.994.5562 or email at johnp@montana.edu
