title: Effects of reduced in utero and post-weaning nutrition on milk yield and composition in primiparous beef cows.
abstract: Development and long-term retention of replacement beef females in a semi-arid environment are of a major concern for extensive livestock producers. Furthermore, the demand of not only producing a thriving, healthy calf, but having sufficient milk to support that first calf is essential. To address this issue, we conducted a 3-year study measuring milk production and milk constituent yields in primiparous beef heifers (n=48; 16/year reared under two different feeding regimens) raising steer calves. Cows received 1.8 or 1.2 kg/day winter supplementation for ~80 day before parturition and their heifer calves were then randomly assigned to heifer development treatments that provided ad libitum (AL) or 80% (less than ad libitum (LAL)) of ad libitum feed post weaning. Heifers developed on the AL treatment also received 1.8 kg/day winter supplementation for life, whereas heifers developed on the LAL treatment received 1.2 kg/day winter supplementation for life. Milk production of primiparous cows was measured with a portable milking machine every other week from days 27 to 125 postpartum. Milk yield for the 125-day lactation period was calculated from area under the lactation curve approximated by trapezoidal summation. The ANOVA model included in utero winter nutrition, post-weaning heifer development treatment, year and their interaction. Heifers subjected to the AL treatment reached peak milk yield ~12.3 day later (P=0.02) than heifers receiving LAL treatment. In addition, an in utero nutrition×post-weaning heifer treatment×year interaction existed (P⩽0.04) for milk peak yield, average daily milk yield (kg/day) and nutrient composition (protein, lactose, fat, solids non-fat, g/day). These interactions manifest as changes in magnitude and rank across the 3 years of the study. Livestock production in extensive environments is subject to variations in seasonal precipitation patterns and quality and quantity of grazeable forage and these fluctuations have a large impact on milk yield. In summary, the gestational nutritional environment of a heifer's mother may interact with the heifer's nutrient consumption during post-weaning growth and the current year to trigger variation in year-to-year milk production.
authors.affiliation: USDA-ARS,Fort Keogh Livestock and Range Research Laboratory,243 Fort Keogh Road,Miles City,59301-4016 MT,USA.
authors.forename: R C
authors.initials: RC
authors.lastname: Waterman
authors.affiliation: USDA-ARS,Fort Keogh Livestock and Range Research Laboratory,243 Fort Keogh Road,Miles City,59301-4016 MT,USA.
authors.forename: T W
authors.initials: TW
authors.lastname: Geary
authors.affiliation: USDA-ARS,Fort Keogh Livestock and Range Research Laboratory,243 Fort Keogh Road,Miles City,59301-4016 MT,USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Petersen
authors.affiliation: USDA-ARS,Fort Keogh Livestock and Range Research Laboratory,243 Fort Keogh Road,Miles City,59301-4016 MT,USA.
authors.forename: M D
authors.initials: MD
authors.lastname: MacNeil
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004032:Diet / Q000662:veterinary*; D019587:Dietary Supplements; D005260:Female; D007774:Lactation / Q000502:physiology*; D008297:Male; D039382:Maternal Nutritional Physiological Phenomena; D008892:Milk / Q000737:chemistry*; D010298:Parity; D049590:Postpartum Period; D011247:Pregnancy; D039401:Prenatal Nutritional Physiological Phenomena; D012621:Seasons; D014886:Weaning
keywords: heifer development; milk and constituent yield; primiparous beef cow