title: Nutritionally altering weight gain patterns of pregnant heifers and young cows changes the time that feed resources are offered without any differences in production.
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 approximately 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 from each other either as heifers (P = 0.23) or as second-parity cows (P > 0.59). The 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), weight of calf weaned (P = 0.50), or 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), weight of calf weaned (P = 0.63), or 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.
authors.affiliation: ARS, USDA, U.S. Meat Animal Research Center, Clay Center, NE 68933, USA. freetly@email.marc.usda.gov <freetly@email.marc.usda.gov>
authors.forename: H C
authors.initials: HC
authors.lastname: Freetly
authors.forename: C L
authors.initials: CL
authors.lastname: Ferrell
authors.forename: T G
authors.initials: TG
authors.lastname: Jenkins
mesh_terms: D000821:Animal Feed; D000822:Animal Husbandry / Q000379:methods; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001835:Body Weight / Q000502:physiology*; D002417:Cattle / Q000254:growth & development* / Q000502:physiology; D004435:Eating / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D005298:Fertility / Q000502:physiology*; D010298:Parity; D011247:Pregnancy; D011897:Random Allocation; D013997:Time Factors; D015430:Weight Gain / Q000502:physiology