Effect of virginiamycin on milk yield and composition under commercial conditions in Mexico

G. VELASCO; A. E. RELLING; GOROCICA M

Knoxville

Congreso; 2018 American Dairy Science Association® Annual Meeting; 2018

line"><The objective of the present study was to evaluate the effect of virginiamycin (VM) inclusion on milk yield and composition in Holsteincows maintained under commercial conditions in Mexico. Four pens oflactating cows (approx. 100 cows each) were blocked based on lactationnumber (LN), DIM, and milk yield (2.1 and 2.3 LN; 190 and 115 DIM;and, 47.3 and 48.5 L/d, for blocks 1 and 2 respectively) and assignedto 2 treatments. Control cows (CT) were fed a diet balanced to meetor exceed their nutrient requirements (NRC, 2001); Treated cows (TR)were fed the CT diet plus 500 mg/cow/d of VM. Diets were randomlyassigned within each block. Diets were based on corn silage and steamflked corn. Feed offered and refused was weighted and analyzed dailyto determine pen DMI. The study lasted for 42 d; d 1?19 for adaptation,and d 20?42 to measure milk yield and composition. Individual milkrecords were obtained daily. Additionally, one pooled milk sampleper pen was collected for milk fat and protein determination using aMilkoScan Mars equipment (FOSS, Hillerød, Denmark). A mixed modelanalysis with repeated measures was conducted at the end of the trial.Pen was the experimental unit. The model included treatment as fiedeffect and block as random effect. No cows were diagnosed with clinicalacidosis during the course of trial and no day × treatment interactionswere observed (all P > 0.10). However, milk yield, milk fat, and ECMwere signifiantly greater in the TR group (P < 0.01; Table 1). TR cowstended to have greater DMI but milk:feed ratio was not affected bytreatment (P > 0.10). Milk fat:protein ratio was signifiantly increased(P < 0.01) suggesting the effects on milk yield and composition mayhave been related to VM preventing the development of SARA andother related digestive disorders.e">Table 1 (Abstr. T178). Milk yield, composition, ECM yield, and DMI duringthe measurement periodItem CT TR SEMTreatment effectP-valueMilk yield, L/d 42.7 43.3 0.25 <0.01Milk fat, % 3.43 3.49 0.120 <0.01Milk protein, % 3.30 3.28 0.004 <0.01ECM1, kg/d 42.8 43.7 0.16 <0.01Fat:Protein 1.04 1.06 0.003 <0.01DMI, kg/d 27.4 27.8 0.20 0.08Milk:DMI 1.57 1.56 0.011 0.671ECM, lb = 0.327 × Milk yield, lb + 12.95 × Fat yield, lb + 7.65 × Proteinyield, lb