عنوان مقاله [English]
Introduction Zinc is part of more than 300 enzymes involved in immunity, metabolism, growth and reproductive functions. This element is essential for the metabolism of nucleic acids, proteins, carbohydrates, the development and proper functioning of immune cells. Therefore, zinc deficiency can affect the performance of animals by reducing appetite and growth and immune system disorders.
Fat supplementation in milk replacer or starter diets has been suggested to improve the energy density of calf diets. Linoleic and alpha-linolenic are two essential fatty acids precursors of eicosanoids, important molecules in regulation of inflammation. Eicosanoids derived from linoleic acid has the inflammatory effects, while Eicosanoids derived from alpha-linolenic acid has anti-inflammatory effects. Adding alpha-linolenic acid in the form of Ca-salt of flaxseed oil to calf starter improves daily weight gain and feed efficiency. It seems to decreasing the ratio of linoleic acid to alpha linolenic acid in the diet have positive effects on the health and immune system of dairy calves.
Zinc has a direct effect on modulating the activity of desaturase enzymes in fatty acid metabolism and also indirectly affects the absorption, oxidation and composition of fatty acids. In addition, zinc participates in the structure of superoxide dismutase, which is an important enzyme in the oxidative process of lipids. Free radicals reaching the cytoplasm are neutralized by this enzyme. The aim of this study was to evaluate the effect of organic supplementation of zinc and dietary Ca-salt of flaxseed oil on growth performance, health status and some blood parameters of Holstein calves.
Materials and Methods A total of Twenty-eight 3-day-old female Holstein calves with a starting average weight of 35.7±2 kg were used in a completely randomized design with a 2×2 factorial arrangement of treatments and 7 replications per treatment for 49 days (before weaning). The experimental treatments were: 1) Control (CON), 2) diet containing 0.1% Zn-methionine supplement (+Zn), 3) diet containing 2.5% Ca-salt of flaxseed oil supplement (+Fat) and 4) diet containing 2.5% Ca-salt of flaxseed oil supplement with 0.1% Zn-methionine supplement (+Fat +Zn). The calves were housed in individual pens and fed with whole milk and had free access to the feed starter and water. Milk was offered 4 L/d in two equal meals daily at 07:00 and 19:00. All the calves were weighed at the beginning of the experiment and days 14, 28, 42 and 49. Daily weight gain and feed efficiency (gain to feed) were calculated. Apparent digestibility was determined by the internal marker method of acid-insoluble ash. Changes in skeletal growth and health scores from birth to 42 days were recorded. Blood samples were collected from the jugular vein on last week of the trial (3 h after the morning feeding). Blood parameters data were analysed using the PROC GLM procedure of SAS (9.1v). Repeated measured data (body weight, feed intake and feed efficiency) were analysed using the PROC MIXED procedure and health scores were analysed using a multivariable logistic mixed model (GLIMMIX). Significance among treatments was determined by the Tukey test and results were considered as significant the P-value was less than 0.05.
Results and Discussion The results showed that the use of Zn-methionine and Ca-salt of flaxseed oil had no significant effect on dry matter intake and growth performance. Daily weight gain tended to increase from day 29 to day 49 in treatments containing fat supplement. Fat supplementation increased dry matter and organic matter apparent digestibility. Addition of zinc-methionine supplement to diets had no effect on apparent nutrient digestibility. Skeletal growth indices did not affect by dietary treatments. Attitude score, nasal discharge, days with fever, days with diarrhea and days with poor attitude were not affected by experimental treatments. Ca-salt of flaxseed oil reduced rectal temperature and improved fecal consistency. Organic Zn did not improve calf health status. Decreased rectal temperature as a result of consuming the source of alpha-linolenic acid may be due to the effects of alpha-linolenic acid and its derivatives eicosanoids in reducing the incidence of inflammatory responses. Interaction among fat and Zn-methionine tended to affect alanine aminotransferase enzyme concentration. Zn-methionine supplement increased the concentration of alkaline phosphatase. Alkaline phosphatase has four Zn element in its active site. This enzyme is involved in calcium absorption and animal growth and is considered as indicator of Zn status. The increase in alkaline phosphatase concentration in the present study can be attributed to the increase in zinc uptake from the source of the organic zinc-methionine.
Conclusion It seems that feeding of Ca-salt of flaxseed oil with high levels of unsaturated fatty acids in dairy calves have a positive effect on calf health status and apparent feed digestibility.