Effect of feed additives in protein supplements on reproductive performance in young postpartum cows

Reproductive performance in young beef cows is often compromised due to a mismatch of physiological demands and suboptimal environmental conditions to support the increase nutrient requirements. Previous research has illustrated that increasing the post-ruminal supply of glucose can partition nutrients away from lactation, which results in decreased days to resumption of estrus and improved pregnancy rates in young range cows. This study was conducted over a three-year period (2019 – 2021) utilizing two- and three-year-old cows (n = 189) from the March-calving herd at the University of Nebraska Gudmundsen Sandhills Laboratory (GSL) located near Whitman, NE. Postpartum supplementation was provided at a rate of 2 lb/d of a 30 % crude protein supplement with the addition of either: 1) 160 milligrams per cow per day of rumensin (MON; Elanco Animal Health) or 2) 40 grams per cow per day of a propionate salt product called NutroCal 100 (CAP; Kemin Animal Nutrition and Health). Supplementation started approximately 10 d after parturition and continued through the first of June for an average of 70 days postpartum. Cow body weight and body condition score were not influenced by postpartum supplemental treatments at all measurement points from calving to weaning. Similarly, calf body weight and ADG were not influenced by supplemental treatments of their dam. In addition, 24-h milk production was not different between cows receiving either CAP or MON. However, overall pregnancy rates were greater in cows receiving CAP (89% pregnancy rate) compared to cows receiving MON (80% pregnancy rate). The results from this study indicated that supplying a protein supplement with the addition of either rumensin or calcium propionate did not improve cow body weight or BCS. However, addition of 40 grams per day of a propionate salt in a protein supplement resulted in increased pregnancy rates in young range cows. These results illustrate how reproductive performance can be uncoupled from changes in body weight or condition score. In addition, supplemental packages designed to provide metabolically potent feed additives can be strategically fed at small amounts can positively alter important economic production traits such as conception date and overall pregnancy rates.

This study was conducted by Tasha King as part of her PhD research working for Dr. Travis Mulliniks.