Effects of replacing sulfate with hydroxychloride sources of trace minerals on health and reproduction in dairy cows.

Trace minerals such as Cu, Mn, and Zn are essential for tissue integrity, antioxidant defense, and immune function, and inadequate intake of minerals might predispose cows to health disorders, especially during the transition period when oxidative stress and inflammation originating from calving increase susceptibility to post-calving diseases. Additionally, it is that not only the amounts consumed, but also the sources of trace minerals that can affect tissue concentrations. However, in official guideline documents no distinctions are made whether the metal is in a sulphate or chloride salt format, despite that these sources differ in solubility. It is logical that providing sources of trace minerals that are more stable in the rumen with potentially less antagonistic interactions, might minimize effects on digestion and improve the subsequent availability for absorption in the intestine; features that might be advantageous particularly when intake of nutrients is limited, such as in early lactation. Thus, altering the source of trace minerals may influence animal responses, but as trace minerals are mostly supplied in the sulphate form, limited data exist on the effects if they are supplied in the hydroxychloride form to transition dairy cows, and almost no information on cow health or reproduction. Thus, the objectives of the cited study were to evaluate the effects of replacing sulphate with hydroxychloride sources of trace minerals on the risk of disease during first 105 days post-calving and on the reproduction and survival of cows during the total 305-day period.

A total of 141 Holstein cows were stratified by calving group pre-calving as either first-calving or multi-calving and, within calving group, first-calving cows were blocked by genomic breeding value for energy-corrected milk (ECM) yield and multi-calving cows by their recently completed lactation 305-day ECM. Within block, the cows were assigned to a group receiving sulphate trace minerals (STM) or a group receiving hydroxychloride trace minerals (HTM), with the pre-calving diets containing 15 ± 1, 58 ± 2, and 66 ± 3 mg/ kg of diet DM as Cu, Mn, and Zn, respectively, whereas the post-calving diets contained 19 ± 3, 65 ± 15, and 77 ± 11 mg/kg diet DM as Cu, Mn, and Zn, respectively. The treatments were fed from 246 days of gestation to 105 days in milk(DIM). The concentrations of non-esterified fatty acids (NEFA), β-hydroxy butyrate (BHB), haptoglobin, and ceruloplasmin were measured in plasma, and those of total calcium (tCa) were measured in serum. Diseases were diagnosed in the first 105day post-calving and survival was evaluated until 305 days in milk (DIM). The oestrous cycle of the cows was synchronized and artificial insemination (AI) was performed on day 87 post-calving. On day 19 after AI, the serum was analysed for progesterone and blood mononuclear cells, and the cervical cells were analysed for mRNA for interferon-stimulated genes (ISG).

Treatment did not affect the concentrations of NEFA, BHB, tCa, and progesterone in the blood. Feeding HTM reduced the concentrations of haptoglobin in the first 19 days post-calving (40.0 ± 9.1 vs. 25.7 ± 5.0 μg/mL) and that of ceruloplasmin only on day 6 post-calving (0.64 ± 0.03 vs. 0.58 ± 0.03 mg/mL). Feeding HTM also reduced the risk of retained placenta (11.5% ± 6.3% vs. 3.8% ± 2.3%) and tended to reduce the risks of clinical (16.4% ± 9.7% vs. 4.0% ± 2.9%) and subclinical endometritis (29.8% ± 9.2% vs 16.4% ± 5.7%). The cows fed HTM tended to have a reduced rate and risk of morbidity during the first 105 days post-calving compared to cows fed STM. Feeding HTM increased the relative expression of ISG by 1.7 to 2.0-fold in blood mononuclear cells on day 19 after AI in pregnant cows compared with STM; however, treatment did not affect the expression of ISG in cervical cells. Rate of pregnancy did not differ between treatments, but HTM tended to increase the proportion of pregnant cows by 305 days post-calving (82.8% ± 4.7% vs 68.8% ± 5.7%), partially attributed to the reduced proportion of cows designated as ‘’do not inseminate’’ (25.6% ± 5.3% vs. 9.8% ± 3.6%). In addition, HTM reduced the rate and risk of leaving the herd by 305day post-calving from 26.5% ± 9.6% in STM to 11.9% ± 5.0%.

Summarised results and interpretation: By feeding hydroxychloride instead of sulphate sources of Cu, Mn, and Zn, reduced the systemic inflammation in early post-calving and the risk and rate of morbidity because of less uterine diseases. Although morbidity in early lactation was linked with increases in acute phase response, only minor associations were found between the concentration of trace minerals in serum and the risk of disease. The mechanisms by which HTM reduced disease, might be mediated by effects unrelated to the bioavailability of the minerals or their concentrations in tissues. The rate of pregnancy did not differ between treatments, but feeding HTM increased the relative expression of ISG in peripheral blood mononuclear cells on day 19 of gestation and the proportion of cows pregnant by 305 DIM. The increased pregnancy was, in part, attributed to the reduced risk of being designated “do not inseminate” and rate of leaving the herd. Because feeding HTM reduced morbidity, it is plausible to suggest that other responses evaluated, such as reproduction and survival, might have been consequences of improved pre-calving health. Nevertheless, the underlying reasons for the reduced risk of retained placenta and other uterine diseases in cows fed HTM compared with STM remain unclear.

Final comment: By replacing sulphate sources of Cu, Mn, and Zn with hydroxychloride sources should benefit the health of cows early post-calving, which should carry through to benefit overall reproduction and survival.