Graduate Thesis Or Dissertation
 

Nutritional Management of Beef Cows During Late-Gestation to Enhance Offspring Productivity

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  • Two experiments evaluated nutritional management of late-gestating beef cows to enhance offspring productivity. The objective of experiment 1 was to evaluate the effects of organic and inorganic Cu, Mn, Zn, and Co supplementation to beef cows during late-gestation on performance and physiological responses of the offspring. The objective of experiment 2 was to evaluate the effects of rumen-protected essential fatty acid (EFA) supplementation to beef cows during the last trimester of gestation on performance and physiological responses of the offspring. In experiment 1, 84 multiparous, non-lactating, pregnant Angus × Hereford cows were ranked by pregnancy type (AI = 56 and natural service = 28), BW, and BCS, and allocated to 21 drylot pens at the end of their 2nd trimester of gestation (day 0). Pens were assigned to receive forage-based diets containing: 1) sulfate sources of Cu, Co, Mn, and Zn (INR), 2) an organic complexed source of Cu, Mn, Co, and Zn (AAC; Availa®4; Zinpro Corporation, Eden Prairie, MN), or 3) no supplemental Cu, Co, Mn, and Zn (CON). Diets were offered from day (d) 0 until calving and formulated to meet requirements for energy, protein, macrominerals, Se, I, and vitamins. The INR and AAC diets provided the same daily amount of Cu, Co, Mn, and Zn. Cow BW and BCS were recorded, and liver samples were collected on d -10 and 2 weeks (wk; d 75) before the calving season. Within 3 h after calving, calf BW was recorded, liver samples were collected, and the expelled placenta was retrieved (n = 47 placentas). Calves were weaned on d 283 of the experiment, preconditioned for 45 d (d 283 to 328), transferred to a growing lot on d 328, and moved to a finishing lot on d 440 where they remained until slaughter. Liver Co, Cu, and Zn concentrations on d 75 were greater (P ≤ 0.05) for INR and AAC compared with CON cows, whereas INR had reduced (P = 0.04) liver Co but greater (P = 0.03) liver Cu compared with AAC cows. In placental cotyledons, Co concentrations were greater (P ≤ 0.05) in AAC and INR compared with CON cows, whereas Cu concentrations were only increased (P = 0.05) in AAC compared with CON cows. Calves from INR and AAC had greater (P < 0.01) liver Co concentrations at birth compared with calves from CON cows. Liver Cu and Zn concentrations at birth were greater (P ≤ 0.05) in calves from AAC compared with cohorts from CON cows. Weaning BW was greater (P ≤ 0.05) in calves from AAC compared with cohorts from CON cows, and this difference was maintained until slaughter. In the growing lot, calves from AAC cows had reduced (P < 0.01) incidence of bovine respiratory disease compared with CON and INR cohorts. In experiment 2, 96 multiparous, non-lactating, pregnant Angus × Hereford cows were stratified by BW and BCS, and divided into 24 groups of 4 cows/group at the end of their 2nd trimester of gestation (d -7). All cows became pregnant during the same estrus-synchronization + AI protocol, with semen from a single sire. Groups were randomly assigned to receive (as-fed basis) 452 g/cow daily of soybean meal in addition to 1) 200 g/cow daily of rumen-protected EFA mix based on eicosapentaenoic, docosahexaenoic, and linoleic acids or 2) 200 g/cow daily of rumen-protected SFA + MUFA mix based on palmitic and oleic acids (CON). Groups were maintained in 2 pastures (6 groups of each treatment/pasture), and received daily 10.9 kg/cow (as-fed basis) of grass-alfalfa hay. Groups were segregated and offered treatments 3 times/week from d 0 until calving. Cow BW and BCS were recorded, and blood samples were collected on d -7 and within 12 h after calving. Calves BW were also recorded within 12 h of calving. Calves were weaned on d 280 of the experiment, preconditioned for 45 d (d 280 to 325), transferred to a growing lot on d 325, and moved to a finishing lot on d 445 where they remained until slaughter. At calving, EFA-supplemented cows had greater (P < 0.01) proportion (as % of total plasma fatty acids) of PUFA including linoleic, linolenic, arachidonic, docosapentaenoic, and docosahexaenoic acids. At weaning, calves from CON-supplemented cows were older (P = 0.03), although no treatment differences were detected (P = 0.82) for calf weaning BW. During both growing and finishing phases, ADG was greater (P ≤ 0.06) in calves from EFA-supplemented cows. Upon slaughter, HCW and marbling were also greater (P ≤ 0.05) in calves from EFA-supplemented cows. Collectively, these results are suggestive of programming effects on postnatal offspring health and productivity resultant from EFA or organic Co, Cu, Mn, and Zn supplementation during last trimester of gestation. Hence, organic trace mineral and EFA supplementation during late-gestation should be considered as feasible nutritional strategies to enhance productivity in beef production systems.
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