Level of supplemental fat in the diet of gestating beef cows: Effects on cow and calf performance.


Cornand E, Larson K, Fitzsimmons C, McKinnon JJ, Lardner HA. 2023. Level of supplemental fat in the diet of gestating beef cows: Effects on cow and calf performance. Poster and presentation at the joint ASAS-CSAS-WSASAS Annual Meeting, Albuquerque, Canada. July 2023.

Plain language summary

Supplementation of cattle during the latter half of pregnancy with a canola fat pellet did not affect cow performance in terms weight gain and rib/rump fat, milk fat or energy, nor calf birth weights, but tended to improve cow pregnancy and calving rate.


This study evaluated the effects of level of fat from a canola seed pellet (7.2% ether extract) in the diet of gestating beef cows on cow performance, reproductive efficiency, milk yield and composition, and calf birth weight. Seventy-two pregnant, multiparous Angus cows were allocated to 12 pens in a completely randomized block design, body weight (BW; 605 ± 35 kg) was utilized as a criterion for block formation. Diets were formulated to be isonitrogenous (CP: 8.20 ± 0.24% second, 9.07 ± 0.05% third trimester) and isocaloric (TDN: 58.29 ± 0.24% second, 60.50 ± 0.04% third trimester) and meet nutrient requirements for the last two trimesters of gestation. Pens were randomly assigned to the following replicated (n=4) dietary treatments (dry matter basis): 0 (CON), 150 (LOW), and 300 (HIGH) g of fat/d. Cows were fed the dietary treatments from 148 ± 8 d prepartum until more than 50% of the cows had calved and then switched to a common lactating diet at 3 ± 8 d prepartum. Milk samples were collected at 21 d and 42 d postpartum and analyzed for fat, protein, lactose, total solids, and milk urea-N (MUN). Orthogonal contrasts were used to assess linear and quadratic relationships between fat inclusion and dependent variables. At the start of trial (SOT), there were no differences (P≥0.73) in conceptus corrected BW (597 ± 34 kg) and (P≥0.13) in body condition score (BCS; 2.85 ± 0.12, Canadian System: 1 to 5). After 84 d on trial (64 ± 8 d prepartum), conceptus corrected average daily gain (ADG) was affected linearly (P=0.04) as fat inclusion increased. However, after 151 d of supplementation (end of trial (EOT)), conceptus corrected ADG did not differ (P≥0.71). Fat inclusion did not affect (P≥0.63) subcutaneous fat thickness. BCS change from SOT to EOT (P=0.02) and EOT to 21 d postpartum (P=0.01) were affected quadratically by fat inclusion. Female calf birth weight was affected (P=0.01) quadratically as fat inclusion increased, with no effect (P≥0.75) on male calf birth weight. As fat inclusion increased, lactose concentration decreased linearly (P=0.04). As days in milk (DIM) increased, lactose yield (P=0.01), milk energy yield (P=0.05), protein (P≤0.01), and total solids (P≤0.04) decreased. MUN tended to increase (P=0.07) while 12 h milk yield (P=0.05) tended to decrease as DIM increased. Milk fat and energy were not affected by fat inclusion, day, or the interaction between fat inclusion and day (P≥0.16). There was a quadratic tendency for fat inclusion to effect pregnancy rate (P=0.09) and conception rate (P=0.09). These results suggest that increasing fat inclusion during mid-to-late gestation did not affect cow performance or calf birth weights but tended to improve cow pregnancy and calving rate.

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