Supplementation of monensin and Optimase to beef cows consuming low-quality forage during late gestation and early lactation

Monensin supplementation during late gestation of beef cows alters maternal plasma concentrations of insulin-like growth factors 1 and 2 and enhances offspring preweaning growth

This study evaluated the effects of maternal prepartum supplementation of dried distillers grains (DDG), with or without monensin addition, on maternal performance and physiology and offspring preweaning growth. On day 0 (approximately 197 ± 4 d prepartum), 150 multiparous, Brangus crossbred beef cows were ranked by their initial body weight (BW; 524 ± 51 kg) and body condition score (BCS; 5.0 ± 0.63), and then randomly assigned into one of 15 bahiagrass (Paspalum notatum) pastures (10 cows and 8.1 ha/pasture). Maternal treatments were randomly assigned to pastures (5 pastures/treatment) and consisted of no prepartum supplementation of DDG (NOSUP) or supplementation of DDG at 1 kg/cow/d (dry matter basis; DM) added with 0 mg (SUP) or 200 mg/d of monensin (SUPMO) from days 0 to 77. Effects of maternal treatment and maternal treatment × day of the study were not detected (P ≥ 0.63) for any forage data. Cow BCS on day 35 and near calving (day 77) did not differ (P ≥ 0.19) between SUP and SUPMO cows but both groups had greater (P ≤ 0.001) BCS compared with NOSUP cows. Cow BCS at the start of the breeding season (day 142) and on day 168 were the greatest (P < 0.0001) for SUPMO cows, least for NOSUP cows, and intermediate (P ≤ 0.02) for SUP cows. Maternal plasma concentrations of glucose did not differ (P ≥ 0.25) among treatments. Plasma concentrations of insulin-like growth factor 1 (IGF-1) on day 77 were the least for NOSUP cows (P ≤ 0.05) and did not differ (P = 0.66) between SUP and SUPMO cows, whereas plasma concentrations of IGF-2 on days 35 and 77 were greatest (P ≤ 0.05) for SUPMO cows and did not differ (P ≥ 0.60) between NOSUP and SUP cows. Birth BW of first offspring did not differ (P = 0.77) between SUP and SUPMO calves but NOSUP calves were lighter at birth (P ≤ 0.05) compared with SUP and SUPMO calves. Percentage of cows pregnant with a second offspring did not differ (P = 0.72) between SUP and SUPMO cows and were the least for NOSUP cows (P ≤ 0.05). First offspring BW at weaning (day 325) was greatest (P ≤ 0.05) for SUPMO calves, least for NOSUP calves, and intermediate for SUP calves. Therefore, adding monensin into prepartum DDG supplements for Bos indicus-influenced beef cows did not increase cow prepartum BCS but led to greatest offspring preweaning growth, likely by modulating maternal plasma concentrations of IGF-1 and IGF-2 during gestation.

Effects of monensin inclusion and level of intake in limit-feeding strategies for beef cows

A study was conducted to evaluate the effects of intake management and ionophore inclusion on diet utilization under managed intake conditions in beef cattle. Two experiments utilized common diets fed at 120% (H) or 80% (L) of maintenance with either 0 or 200 mg/d monensin in a factorial arrangement. Forty cows were fed for 56 d (Exp. 1) to evaluate effects on diet utilization and energy retention; diets were fed to 16 ruminally cannulated steers (Exp. 2) to determine effects on digestion, energy value, and ruminal fermentation. Cows fed H had greater body weight (BW) gain (P < 0.01) and retained energy (RE; P < 0.01), although estimated heat production was also greater (P < 0.01). Monensin had limited effects on overall BW gain (P = 0.97). Monensin had no effect on RE (P = 0.94) or calculated heat energy (HE; P = 0.53) despite effects on diet utilization observed in steers. In steers, L increased (P < 0.01) digestion of dry matter, organic matter, acid detergent fiber, and gross energy (GE) and reduced (P < 0.01) passage rate; monensin did not affect digestion (P > 0.15) but did reduce passage rate (P < 0.03). Monensin lowered (P < 0.01) acetate:propionate ratio and increased (P < 0.05) ruminal pH. Monensin did not alter feed required for maintenance; however, limit-feeding reduced apparent daily maintenance requirement to 62.85 kcal/kg BW^0.75, a 26% reduction from model-predicted values.

Hormones and monensin use to improve pregnancy rates in grazing lactating beef cows in the semiarid region of Argentina

The objectives of this study were 1) to determine the effect of monensin treatment, alone or combined with a hormonal estrus synchronization treatment, on the pregnancy rate of lactating beef cows, and 2) to evaluate the effect of monensin capsule administration on ruminal metabolism in steers. In experiment 1, ninety-four cows were selected from a 300 cow herd. The experimental design used was a 2 x 2 factorial with the administration of monensin capsule as first factor (M1 = with monensin vs. M0 = without monensin) and hormonal treatment as second factor (H1 = with hormonal treatment vs. H0 = no hormonal treatment). Thirty-eight days before the beginning of the breeding season, cows were randomly assigned to the first factor, and thirty days later to the second factor, resulting in four treatments: M1H0, M1H1, M0H0 and M0H1. Cow were exposed to bull (bull/cow ratio 1:20) from day 0 (day 0 = start of the breeding season and 38 days after monensin capsule administration) to day 50. Pregnancy diagnosis was performed at 30, 60 and 80 days after start breeding season by ultrasonography. In experiment 2, eight ruminally cannulated crossbred beef steers were randomly assigned to two treatments (M1 and M0). To determine proportion of volatile fatty acids (VFA), ruminal fluid samples were taken on days 0, 40 and 77 of the experimental period, at 0, 4 and 12 h after grazing. In experiment 1, treatments whit monensin did not improve pregnancy rate (P = 0.95), however, hormonal treatment resulted in grater pregnancy rates (P = 0.03). In experiment 2, the proportion of VFA in ruminal fluid of steers was significantly different between treatments. The highest proportion of propionate was found in ruminal fluid from M1 treatment at 12 h after grazing (P = 0.04). In conclusion, the treatment with monensin increased the proportion of propionate. The result might suggest that energy balance was improved in steers, without improvement in cow´s pregnancy rates. Treatment with monensin alone did not improve pregnancy rate, nor did treatment with monensin enhance the pregnancy rate when a hormonal synchronisation treatment was given. Nevertheless, the use of a hormonal treatment increased pregnancy rate, suggesting that it could be used as a suitable tool to enhance the productivity in cows with marginal body condition score.