The effect of sodium chloride supplementation on the milk production of grazing Holstein Friesian cows during summer and autumn in a humid sub-tropical environment

Two studies were conducted to examine the effects of including NaCl at various rates in grain-based supplements for Friesian cows grazing established, dominant (>90%), rainfed kikuyu (Pennisetum clandestinum cv. Common) pastures during summer and autumn in a humid sub-tropical environment. dy 1 (19 January–27 March 1998), 48 cows (36 multiparous, 12 primiparous; 27–96 days postpartum) were allocated to one of four groups based on genetic merit, milk production, liveweight (LW) and days postpartum. They were fed (2.7 kg dry matter (DM) per cow, twice-a-day) one of four isoenergetic and isonitrogenous barley grain-based concentrates containing NaCl at concentrations (% as-fed) of either 0 (SC1), 1.1 (SC2), 2.2 (SC3) or 3.3 (SC4). Maximum temperature humidity index (THImax) was ≥78 during 50% of the experimental period. Concentrate NaCl content had no effect (P>0.05) on daily milk yield or LW change but daily yields of 4% fat corrected milk (FCM), fat and protein were higher (P<0.05) for cows fed SC3 (16.2 kg, 615 g and 494 g, respectively) compared to cows fed the other concentrates (SC1: 14.2 kg and 546 g fat, 450 g protein, respectively; SC2: 15.0 kg and 553 g fat, 461 g protein, respectively; SC4: 14.2 kg and 529 g fat, 454 g protein, respectively). Daily pasture intake was not different (P>0.05) among treatments at 7.6±1.24 kg DM per cow. dy 2 (18 January 1999–1 March 1999), 48 cows (32 pluriparous, 16 primiparous: 32–160 days postpartum) were fed (2.7 kg DM per cow twice-a-day) one of two isoenergetic and isonitrogenous barley grain-based concentrates containing NaCl at concentrations (% as-fed) of 0 (control) or 2.2 (HSC). THImax was ≥78 during 34% of days in the experimental period. Yields of milk, FCM, fat and protein were lower (P<0.05) for cows fed HSC. LW change, milk fat content and milk protein content were unaffected (P>0.05) by concentrate NaCl content. These studies indicate that NaCl supplementation can be beneficial in terms of milk production during warm, humid conditions as opposed to milder conditions.