Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/16/2004
Publication Date: 3/7/2005
Citation: Freetly, H.C., Ferrell, C.L., Jenkins, T.G. 2005. Nutritionally altering weight gain patterns of pregnant heifers and young cows changes the time that feed resources are offered without any differences in production. Journal of Animal Science. 83:916-926. Interpretive Summary: Nutrient requirements of the cow fluctuate through the year depending on the stage of pregnancy and level of milk production. Nutrient availability fluctuates through out the year in grazed forage-based production systems. Seasonal variation in markets and other external factors frequently dictate that matching nutrient requirements to nutrient availability is not always the best economic model. Subsequently, a source of mechanically harvested feed is often used to maintain BW of cows when there is a discrepancy between nutrient requirements and nutrient availability. Supplemental feed frequently is more expensive than grazed feeds. This study has shown that mild nutrient restriction during the second trimester of pregnancy followed by increased feed availability in the third trimester can shift the time in the production cycle that feed resources are used. This study also shows that maintaining light weight cows during pregnancy and increasing feed availability during lactation can be used to decrease annual feed intake and shift the time that feed resources are used. These findings suggest that management strategies that include allowing for weight fluctuation of cows can provide flexibility in the time that supplemental feed is provided to the cow herd.
Technical Abstract: We hypothesized that feed resources could be deferred to a later time in the production cycle without a decrease in fertility or weight of calf produced in heifers and young cows. One-hundred and thirty-one MARC III (four breed composite: 1/4 Hereford, 1/4 Angus, 1/4 Red Poll, and 1/4 Pinzgauer) heifers were divided into three treatments: M-M-M-M (n = 46), L-H-M-M (n = 41), and L-L-L-H (n = 44). The experiment consisted of four feeding periods. Period 1 was 94 to 186 d of gestation and heifers were fed a moderate (M) or low (L) level of feed. Period 2 was 187 d of gestation to parturition and heifers were fed moderate, high (H), or low levels of feed. Period 3 was from parturition through 27 d of lactation and heifers were fed moderate or low levels of feed. Period 4 was from 28 d to ~63 d of lactation and heifers were fed moderate or high levels of feed. Females remained within treatments through their first parity (heifers) and second parity (cows). Feed intake of L-H-M-M and M-M-M-M treatments did not differ between each other either as heifers (P > 0.23) or as second parity cows (P > 0.59). L-L-L-H heifers ate less feed than L-H-M-M and M-M-M-M heifers (P < 0.001), and second parity L-L-L-H cows ate less feed than second parity L-H-M-M and M-M-M-M cows (P < 0.002). In the first parity, treatments did not differ in the percentage of calves weaned (P = 0.11), in the weight of calf weaned (P = 0.50), nor in the percentage of cows diagnosed pregnant (P = 0.29) with a second calf. In the second parity, treatments did not differ in the percentage of calves weaned (P = 0.77), in the weight of calf weaned (P = 0.63), nor in the percentage of cows expressing a corpus luteum at the start of breeding for their third calf (P = 0.21). Our findings suggest that timing nutrient availability to heifers and primiparous cows can be used to change the time that feed resources are used.