Effect of oral administration of cobalt-acetate on rumen fermentation and milk production and composition in dairy goats

Abstract

Stearoyl-CoA desaturase (SCD) plays a key role in the synthesis of fatty acids in the mammary gland of ruminants as it is responsible for the conversion of vaccenic acid (trans-11 18:1) to the potentially health- promoting cis-9, trans-11 CLA, and of stearic acid (18:0) to oleic acid (cis-9 18:1) (Griinari et al 2000). Previous studies (have shown that cobalt (Co) as Co-acetate inhibits SCD activity, but the extent of inhibition is different between cows (Shingfield et al 2008) and sheep (Frutos et al 2014). These interspecies differences were observed not only in milk fat composition but also in terms of susceptibility to intoxication when equivalent doses of cobalt per kg of live weight (LW) were provided. Although goat s response to Co is expected to differ from that of cows or sheep , no studies have been carried out yet. The aim of this study was to examine the effects of oral administration of increased levels of Co-acetate on dry matter intake (DMI), rumen function, and milk production and composition in dairy goats. Twenty four lactating Murciano-Granadina goats (48.3 ± 1.1 kg) were randomly allocated to 4 groups and fed 1.5 kg of concentrate (60%) and alfalfa (Medicago sativa) hay (40%) per day. Animals were adapted to the diet during 21 days followed by a 5 days treatment period in which each group received one of the following doses of Co-acetate: 0 (control), 3, 6 and 9 mg Co-acetate/kg LW and day. Animals have free access to fresh water. Experimental procedures were approved by the EEZ-CSIC Animal Experimentation Ethics Committee and completed in accordance with the Spanish Royal Decree 53/2013 for the protection of animals used for experimental purposes. Dry matter intake and milk production were recorded daily. On the last day of Co-acetate administration, milk samples were collected and analysed for fat, protein, lactose, and fatty acid composition. Additionally, the day after, rumen fluid samples were taken via stomach tube and analysed for pH, ammonia and VFA (volatile fatty acids) concentrations. Results on DMI, milk yield and composition as well as milk fatty acid composition were analysed by one-way ANCOVA. Rumen fermentation data were analysed by one-way ANOVA.

Administration of 9 mg Co-acetate/kg LW and day was stopped on day 4 as most goats in this group showed clinical symptoms of toxicosis (severe depression in intake and milk yield). There was no negative effect of the administration of 3 or 6 mg Co-acetate/kg LW and day on pH (7.09, 6.76 and 6.99 for control and doses 3 and 6 mg/kg LW and day, respectively) ammonia (280, 342 and 360 mg/l) or VFA (51.2, 68.0 and 71.4 mmol/l). However, DMI (1.63, 1.58 and 1.48 kg/d) and, subsequently, milk yield (2.16, 1.87 and 1.46 kg/d), decreased (P < 0.01) in animals receiving 6 mg Co-acetate/kg LW and day in comparison to the control. Although milk composition remained unchanged across treatments, protein (73.7, 61.9 and 52.0 g/d), lactose (108, 90.6 and 70.6 g/d) and total solids (303, 264 and 220 g/d) yields were reduced (P < 0.05) in animals receiving 6 mg Co- acetate/kg LW and day compared with the control. Changes in milk yield and composition were greater than those previously reported for cows and sheep when similar doses were administered (Shingfield et al 2008; Frutos et al 2014), supporting interspecies differences. Despite goats seemed to have a lower tolerance to Co than cows and sheep, preliminary results showed that administration of 3 mg Co-acetate/kg LW and day caused a significant reduction in milk cis-9 18:1/18:0 (35.4%; P < 0.05) and cis-9, trans-11 18:2/trans-11 18:1 (45.2%; P < 0.01) concentration ratios. Therefore further research with this Co-acetate dose would be recommended to study the relevance of SCD in milk fat composition in dairy goats.