F. Bargo

Effects of fat supplementation on milk production and composition by dairy cows on pasture: a review

Abstract Eighteen experiments involving 25 comparisons were reviewed to describe the main effects of fat supplementation on milk production and composition with grazing dairy cows. Results were analyzed comparing the fat supplemented and the control groups without supplemental fat, and were segmented according to the stage of lactation (early- or mid-lactation) and the degree of saturation of the fat supplement (unsaturated or saturated). Fat supplements, both saturated and unsaturated, did not affect ruminal fiber digestion. Pasture and total dry matter intake were not consistently affected by fat supplementation. Milk and 4% fat-corrected milk production were increased by 0.97 and 1.05 kg/cow per day with fat supplementation. Milk response to fat supplementation was higher in mid-lactation cows and when saturated fat sources were fed. Milk fat concentration was increased 5.1% with saturated fat supplementation and decreased 8.0% with unsaturated fat supplementation when compared to control groups. Feeding unsaturated fats increased long-chain unsaturated fatty acids in milk fat including conjugated linoleic acid. Milk protein concentration was reduced by feeding unsaturated fat supplements, although milk protein yield was not affected. The experimental results reviewed suggest that fat supplementation to the diet of dairy cows grazing high-quality pastures generally increases milk production although the effects on milk composition depend on the degree of saturation of the fat supplement.

Milk Production of Dairy Cows Fed Total Mixed Rations After a Grazing Period

Twenty multiparous Holstein cows were used in a completely randomized design with repeated measures to study milk production of cows supplemented or not supplemented with concentrate when they were switched to a total mixed ration (TMR) after grazing. In one group, cows grazed an or-chardgrass/bromegrass pasture and were assigned to one of two treatments: 1) unsupplemented (U; 1 kg/d mineral mix) or 2) concentrate supplemented (CS; 1 kg corn-based concentrate/4 kg milk). Total DMI was greater (26.5 vs 22.0 kg/d), but pasture DMI was less (16.8 vs 21.2 kg/ d), for CS cows because of the substitution rate of 0.49 kg pasture/kg concentrate. Overall, CS cows had greater 3.5% fat-corrected milk (FCM) (32.9 vs 26.5 kg/d), but less milk urea N (MUN; 9.6 vs 14.7 mg/dL) and milk fat (3.13% vs 3.88%), than U cows. Milk response to supplementation averaged 1.08 kg milk/kg concentrate. Cows assigned to both treatments lost BW (-17 kg/d) and body condition score (BCS) (-0.33). At the end of the 6-wk grazing period, all cows were switched to a TMR fed in confinement for 11 wk. Overall, DMI (24.3 kg/d), 3.5% FCM (30.6 kg/d), milk fat (3.26%), milk true protein (2.87%), and MUN (12.7 mg/dL) did not differ between treatments. Cows gained BW (53 kg) and BCS (0.33). A significant treatment × time interaction was found for milk yield. During the first day of TMR feeding, milk yield was greater (30.9 vs 19.3 kg/d) for CS cows. After 10 d on a TMR, milk yields between cows that had previously been on the U or CS treatments did not differ (35.5 kg/d). When cows were switched from only pasture to a TMR, milk yield was comparable with that of cows fed CS after 10 d. Lack of carry-over effects of previous treatments and increased production suggest improvement in nutrition and the potential for greater animal well-being for cows housed in a tiestall barn and fed a nutritionally complete TMR.

Milk Response to Bovine Somatotropin of High Producing Dairy Cows with Three Different Feeding Systems Combining Pasture and Total Mixed Rations

Forty-five Holsteins cows (15 primiparous; 30 multiparous) were used to evaluate the milk response to bovine somatotropin (bST) injections with three feeding systems combining pasture and total mixed ration (TMR) in a 21-wk repeated measures experiment. The three treatments were 1) pasture plus concentrate (PC), 2) pasture plus TMR (pTMR), and 3) TMR (non-pasture). Mean total DMI, estimated using chromic oxide as a fecal marker, was 21.6, 25.3, and 26.8 kg/d for cows fed PC, pTMR, and TMR, respectively. Milk production was greatest for cows fed TMR (38.1 kg/d), least for cows fed PC (28.5 kg/d), and intermediate for cows fed pTMR (32.0 kg/d). Cows fed pTMR and TMR had greater milk fat (3.33% vs 3.13%) and true protein (2.97% vs 2.82%) percentage than cows fed PC. Cows on PC gained less BW and lost more body condition than cows on pTMR and TMR. Ten bST injections were administered during the 21-wk trial. Cows had a milk peak different (P<0.05) from d 1 (injection day) for six of the injections on the PC treatment, for four of the injections on the pTMR treatment, and for nine of the injections on the TMR treatment. Day of peak milk yield postinjection and milk response per day were d 6.4 and 2.6 kg for the cows on the PC treatment, d 7.3 and 2.4 kg for cows on the pTMR treatment, and d 7.1 and 4.0 kg for cows on the TMR treatment, respectively. Overall, milk response to bST was greater for cows on the TMR treatment than for cows on the PC and pTMR treatments (344 vs. 259 kg per cow).