Hydrogenated fish fat for grazing dairy cows in summer

Thirty-two multiparous Holando argentino cows in mid lactation were randoml y assigned to two treatments: control or HFF (hydrogenated fish fat) at Raf aela, 31 degrees 11' South, during summer 1997/1998, to evaluate the effect of using HFF as a supplement under grazing conditions. Animals in both tre atments grazed an alfalfa pasture, and were confined from 1000 hours to 170 0 hours daily in a shaded pen where water was provided ad libitum. During e ach milking, animals in the control group received 3.73 kg dry matter per c ow each day (DM cow(-1) day(-1)) concentrate (15% crude protein; 8.69 MJ en ergy for location/kg DM). Cows in the HFF group received 3.25 kg DM cow(-1) day(-1) concentrate, plus 0.200 kg DM cow(-1) day(-1) HFF. Both diets pres ented similar energy, protein and neutral detergent fibre contents. The tri al was performed during a strong "El Nino" event, which resulted in a total rainfall of 396.3 mm (80% higher than normal). The mean temperature was 23 .7 (SD 3.2)degreesC and the mean temperature humidity index was 72.9 (SD 4. 96). Production data were analysed using a completely randomised design with ana lysis of covariance. Supplementation with HFF produced an increase in daily milk production (26.4 (SD 2.46) 1/cow compared to 23.9 (SD 2.68) 1/cow for the controls; P <0.05). Milk fat production was higher for HFF (P <0.05): 941 (SD 96) g cow(-1) day(-1) as compared to controls, which yielded 846 (S D 95) g cow(-1) day(-1). Milk protein yields also differed significantly (P <0.05), the respective values for HFF and controls being 795 (SD 72) g cow (-1) day(-1) and 715 (SD 83) g cow(-1) day(-1). It was concluded that hydro genated fish fat could be a good ingredient to sustain high yields and elev ated maintenance requirements in a grazing system during hot conditions.