The objectives were to determine the effects of supplemental fat (no oilseed vs. oilseed) during late gestation and the source of fat (canola vs. sunflower seed), on dry matter intake (DMI), plasma metabolite concentrations, milk production and composition, calf birth weight, postpartum health disorders, ovarian function and reproductive performance in dairy cows. Pregnant Holstein cows, blocked by body condition and parity, were assigned to 1 of 3 diets containing rolled canola seed (high in oleic acid; n=43) or sunflower (high in linoleic acid; n=45) at 8% of dry matter, or no oilseed (control; n=43), for the last 35±2 d of pregnancy. After calving, all cows received a common lactation diet. Blood samples were collected at wk -3 (i.e., 2 wk after initiation of prepartum diets) and at wk +1, +2, +3, +4 and +5 postpartum to determine the concentration of fatty acids (mEq/dL), β-hydroxybutyrate (mg/dL), and glucose (mg/dL). Ovarian ultrasonography was performed twice weekly to determine the first appearance of dominant (10mm) and preovulatory-size (≥16mm) follicles, and ovulation. Uterine inflammatory status based on the proportion of polymorphonuclear leukocytes (PMN; subclinical endometritis: >8% PMN) was assessed at d 25±1 postpartum. Significant parity by treatment interactions were observed for DMI and milk yield. Prepartum oilseed supplementation, more specifically sunflower seed supplementation, increased postpartum DMI in primiparous cows without affecting prepartum DMI or milk yield. Contrarily, in multiparous cows, prepartum oilseed supplementation decreased both prepartum and postpartum DMI and milk yield during the first 2 wk. Regardless of parity, prepartum feeding of canola reduced postpartum DMI compared with those fed sunflower. Mean fatty acids concentrations at wk -3 were greater in cows given supplemental oilseed than those fed no oilseeds. Gestation length and calf birth weight were increased in cows given supplemental oilseed prepartum compared with cows fed no oilseeds, and a disproportionate increase in the birth weight of female calves was evident in cows fed oilseed. Total reproductive disorders tended to be greater in cows fed supplemental oilseed than those fed no oilseed (42 vs. 23%). Furthermore, cows fed sunflower seed had greater incidences of dystocia (35 vs. 18%) and total health disorders (52 vs. 32%) than those fed canola seed. Added oilseed and type of oilseed did not affect uterine inflammation at 25±1 d postpartum. Oilseed supplementation did not alter the intervals from calving to establishment of the first dominant follicle, preovulatory-size follicle, and ovulation, nor did it affect fertility (conception rate to first artificial insemination and proportion of pregnant cows by 150 d after calving). In summary, prepartum oilseed supplementation (6.2 to 7.4% ether extract, % of dietary dry matter) decreased DMI during the entire experimental period (pre- and postpartum), decreased milk yield during early lactation in multiparous cows, and increased calf birth weight with no significant improvement in ovarian function and reproductive performance.
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