Influence of different sources of zinc and protein supplementation on digestion and rumen fermentation parameters in sheep consuming low-quality hay

Abstract

This experiment studied the effect of ZnCl2 or ZnSO4 included into a protein supplement on dry matter intake (DMI), DM digestibility (DMD) and rumen fermentation parameters in sheep consuming low-quality native pasture hay (NPH) as a basal diet. Four ruminally fistulated Corriedale weathers (31±4kg BW) were randomly assigned to a 4×4 latin square design, and received NPH ad libitum in the following treatments: (1) Control (CON) mineral mix only, (2) protein supplement (PROT), (3) PROT+ZnCl2 (CZProt) and (4) PROT+ZnSO4 (SZProt). All supplements were fed at the rate of 150ganimald−1. The Zn concentration in CZProt and SZProt was 460ppm for a total intake of 100ppm daily as a proportion of total diet. The NPH contained 5.3 and 77.4 of CP and NDF as % of DM respectively. Protein supplements were isonitrogenous (30% CP) with barley grain, wheat middlings and sunflower meal as main components. Mean NPH intake and total DMI were not affected by protein supplementation or Zn addition to the diet. DM digestibility as well as DDMI (digestible DMI) increased 31 and 37% respectively for SZProt compared to CON (P<0.05). Sampling hour affected most rumen variables with the exception of butyric and total volatile fatty acids (VFA; P<0.05). A treatment by sampling hour interaction (P<0.05) was only found for ruminal ammonia-N (NH3-N) concentration. At time intervals of 2, 4, 8 and 12h, [NH3-N] was much lower in CON than in protein supplemental treatments (P<0.05). A trend was observed for increased NH3-N concentration in SZProt (39.76mgdL−1) vs. CZProt (29.25mgdL−1) at 4h (P=0.0897). The rumen pH was not affected by treatments; the lowest values found 12h after feeding were 6.2. Zinc, particularly from SZProt, seems to modulate [NH3-N] by sustaining higher concentrations during the 24h period. A clear effect on major VFA was not observed. The inclusion of 100ppm of Zn, and source could differentially affect animal response to protein supplementation and utilization of low quality roughages by affecting some rumen fermentation patterns.