Date Full Report Received05/23/2018
Date Abstract Report Received05/23/2018
InvestigationInstitution: Virginia Polytechnic Institute and State University
Primary Investigator: Dr. Mark Estienne Ph.D.
Co-Investigators: Sherrie G. Clark-Deener
Funded ByNational Pork Board
Addition of copper sulfate or zinc oxide to nursery pig diets at levels in excess of dietary requirements was previously shown to enhance growth performance. In the new era of antimicrobial use restrictions, the proportion of farmers incorporating elevated concentrations of these trace minerals in nursery pig diets will likely increase. Both copper and zinc, however, have been reported to inhibit iron absorption and research suggests that high dietary concentrations of zinc oxide are associated with a greater risk of anemia in pigs after weaning. Iron deficiency anemia at weaning is an emerging issue, and it has been suggested that the traditional treatment of pigs early in life with 100 to 200 mg of iron may be insufficient to meet requirements of large, fast-growing individuals, and a second injection of iron may be indicated. The additional iron treatment could be particularly important for nursery pigs consuming diets with elevated levels of copper or zinc, especially during the early post-weaning period. The objectives of the research reported here were to determine the effects of iron injections at weaning on hematology characteristics and growth performance in nursery pigs fed antibiotic-free diets containing elevated levels of copper (Experiment 1) or zinc (Experiment 2). In each experiment, pigs received intramuscular injections of 100 mg iron dextran within 24 hours after birth. At weaning (21 days of age) pigs were classified as large or small and one-half of pigs of each size received a second injection of 100 mg iron. Pigs were placed three pigs/nursery pen, as per a 2 x 2 x 2 factorial arrangement of treatments, main factors being size (large vs. small), iron injections (one vs. two) and diet (control vs. 250 ppm copper [Experiment 1] or 2000 ppm zinc [Experiment 2]) (n = 6 pens/treatment combination in each experiment). Growth performance was measured, and hematology characteristics assessed (one pig/pen) at weaning (day 0) and days 7 and 49 post-weaning. Of 90 pigs blood sampled at weaning in Experiments 1 and 2, more (P < 0.01) large (24/45, 53.3%), compared to small (7/45, 15.6%) pigs were classified as anemic, having hemoglobin concentrations of less than 9 g/dL. For the pigs blood sampled, growth during the first seven days post-weaning was affected (P = 0.04) by an interaction between anemic status and iron treatment at weaning. The average daily gain (ADG) of anemic and non-anemic pigs that received iron treatment at weaning were similar (P > 0.05). In contrast, non-anemic pigs not receiving an iron treatment at weaning had greater (P < 0.05) ADG compared to their anemic counterparts. Over the course of the entire trial, ADG was not affected by anemic status, number of iron treatments, or the interaction between these factors. Consistent with the hypothesis that elevated levels of copper negatively impact iron absorption, in Experiment 1, hemoglobin concentrations (P = 0.02), and hematocrit (P = 0.02), were greater in pigs fed control diets (11.4 ± 0.3 g/dL and 37.5 ± 0.9%, respectively) compared to pigs fed diets containing 250 ppm copper (10.8 ± 0.3 g/dL and 35.7 ± 0.9%, respectively). From day 0 (weaning) until day 7 post-weaning, ADG and GF were affected (P = 0.04) by an interaction between treatment at weaning (in other words, iron or no iron) and diet (copper-supplemented or control). For pigs fed the copper diet, animals treated with iron at weaning had greater (P < 0.05) ADG and GF than animals not treated with iron. The additional iron treatment at weaning had no effect (P > 0.05) on ADG or GF in pigs consuming the control diet. From day 0 until day 49 post-weaning (entire trial), ADG (P = 0.02) and ADFI (P = 0.04) were affected by an interaction between iron treatment and diet. For pigs fed the copper diet, animals treated with iron at weaning had greater (P < 0.05) ADG and ADFI than animals not treated with iron. The additional iron treatment at weaning had no effect (P > 0.05) on ADG or ADFI in pigs consuming the control diet. From day 0 to 7 in Experiment 2, zinc-fed pigs had greater (P < .01) ADG and GF, but similar (P = .14) ADFI compared to controls. Over the course of the 49-day trial, pigs fed diets supplemented with zinc had greater ADFI (P < .01) but similar ADG (P = .44) and GF (P = .23) compared with controls. In contrast to Experiment 1, there was no interaction of the zinc diet and number of iron treatments. Research conducted by our team has demonstrated that: 1) Consistent with previous work at Virginia Tech and other institutions, a significant proportion of pigs are anemic at weaning, despite having received i.m. iron shortly after birth; 2) Within litters, the larger, faster growing individuals are most likely to be anemic; and 3) The enhanced growth performance in response to high levels of copper, but not zinc, added to antibiotic-free diets is dependent on an adequate iron status in the weaned pig. Contact: Mark J. Estienne, Ph.D. 757-807-6551 or firstname.lastname@example.org.