The effects of a clay mineral-based feed additive on metabolism and inflammation in heat-stressed lactating dairy cows.

Abstract

Study objectives were to determine the effects of a dietary clay mineral-based feed additive on performance, metabolism, inflammation, and liver and gastrointestinal health in acutely heat-stressed lactating dairy cows. Primiparous Holstein cows (148 ± 25 DIM; 600 ± 50 kg BW; n = 12) were balanced by DIM and milk yield and assigned to 1 of 2 ad libitum fed treatments: 1) control (CON; 500 g ground corn/d; n = 6), or 2) clay mineral-based mycotoxin binder (CM; 500 g ground corn and 50 g of Biofix®/d; n = 6). Respective treatments were top-dressed into the individually fed TMR and the mycotoxin quantities naturally found in the TMR were considered low. Following 3 d of acclimation to individual pens, cows were enrolled in 2 experimental periods (P). During P1 (10 d), cows were housed in thermoneutral (TN) conditions and fed their respective dietary treatments. During P2 (7 d), heat stress (HS) was induced using individual electric heat blankets (EHB, Thermotex Therapy Systems Ltd., Calgary, AB, Canada). Regardless of diet, HS increased rectal temperature and respiration rate (1.9°C and 54 breaths/min, respectively), and decreased DMI and milk yield (45 and 35%, respectively) relative to P1. Heat stress decreased circulating glucose and glucagon similarly in both treatments (6 and 21%, respectively). Overall, circulating insulin tended to be increased in CM-fed cows (36 and 54%, in P1 and P2, respectively). Plasma NEFA and BUN concentrations increased (70 and 41%, respectively) during HS, but neither metabolite was affected by dietary treatment. Although circulating cortisol was unaffected by HS, fecal cortisol metabolites increased (3.4-fold) similarly between diets. Circulating lipopolysaccharide binding protein and haptoglobin increased on d 1 of HS relative to P1 (1.4- and 27.8-fold, respectively), but no dietary differences were observed. Relative to P1, HS increased circulating serum amyloid A (SAA) in CM-fed cows (7.0-fold) on d 1, while it was unaffected by HS in CON, which suggests CM might have immunomodulatory effects. Following d 1 of HS, SAA returned to P1 levels in CM-fed cows, and both treatments had similar SAA levels for the remainder of P2. In summary, HS markedly reduced milk production and caused an acute phase protein response, and while feeding CM did not ameliorate the production responses, it did influence insulin and SAA. Further investigation on the potential role of clay mineral-based feed additive(s) during a longer and less severe HS and when cows are fed a more mycotoxin-contaminated TMR is warranted.