SummaryThe aim of this study was to assess the effects of particle size (PS) of alfalfa hay on growth characteristics and rumen development in dairy calves at two levels of alfalfa supplementation. Fifty newborn dairy calves (42.7 AE 2.2 kg BW) were used in a 2 9 2 factorial arrangement with the factors supplementation level (low, 8%; or high, 16% on DM basis) and PS (medium, 2.92 mm; or long, 5.04 mm as geometrical means) of alfalfa hay. In addition, a control group without alfalfa hay was used. Hence, treatments were: control (C); low level with medium PS (LM); low level with long PS (LL); high level with medium PS (HM) or high level with long PS (HL). Growth performance of alfalfa-fed calves did not differ from control calves, but alfalfa supplementation decreased corneum thickness of the rumen wall. In alfalfa-fed calves, post-weaning starter intake was greater for LL calves than for LM calves. During the entire rearing period, starter intake was 26-32% higher for LL and HM calves than for LM calves. Pre-weaning average daily gain was higher for LL and HM calves than for HL calves, but this effect was not persistent over the entire rearing period. Final body weight decreased from 86 to 79 kg when the level of long PS alfalfa hay increased from 8 to 16%, but increased from 78 to 87 kg when the level of medium PS alfalfa increased from 8 to 16%. Regardless of PS and level, morphometric characteristics of rumen wall were generally similar among alfalfa feeding groups, but corneum thickness decreased from 8.7 to 6.1 lm with greater PS at the low level. These results indicate that adequate, but not excessive, physical stimulation is required for appropriate rumen development and growth performance of dairy calves.

Introducing forage in the young calf diet during the milk-feeding period stimulates rumen development. It was hypothesized that performance in dairy calves would depend on forage provision and starter physical form such that the textured starter (TS) feed with corn silage (CS) supplementation would benefit calf performance. This study evaluates the effects of the physical form of starter diets and CS supplementation on performance, rumen fermentation characteristics, and structural growth of dairy calves. Forty-eight 3-d-old Holstein dairy calves with a mean starting BW of 42.1 kg (SD 2.4) were used in a 2 × 2 factorial arrangement with the factors dietary CS level (0 or 15% on DM basis) and physical form of starter (mashed vs. textured). Individually housed calves were randomly assigned ( = 12 calves per treatment: 6 males and 6 females) to 4 treatments: 1) a mashed starter (MS) feed with no CS (MS-NCS), 2) a MS feed with CS (MS-CS), 3) a TS feed with no CS (TS-NCS), and 4) a TS feed with CS (TS-CS). The calves had ad libitum access to water and starter throughout the study. All calves were weaned on d 56 of age and remained in the study until d 66. The interaction of the physical form of the starter and CS provision was significant ( < 0.01) for the starter intake, with the greatest intake for TS-CS treatment during the preweaning and overall periods. Regardless of the physical form of starter, starter intake, ADG, weaning BW, final BW, ruminal pH, the molar proportion of acetate, and the acetate-to-propionate ratio were greater ( < 0.01) for CS-supplemented calves compared with unsupplemented calves. No interaction ( > 0.05) was detected between the physical form of starter and CS provision with respect to the rumen fermentation parameters and body measurements. Total rumen VFA concentration and the molar proportion of propionate were greater ( < 0.01) in calves fed TS compared with MS-fed calves. In conclusion, independent of the physical form of starter, inclusion of 15% CS in starter diets improves the performance of dairy calves.

Reactive nitrogen species include nitric oxide (.NO), peroxynitrite (ONOO(-)) and nitrogen dioxide radical (NO2*). Peroxynitrite is a reactive oxidant, produced from nitric oxide (*NO) and superoxide anion (O(2*-), that reacts with a variety of biological macromolecules. It is produced in the body in response to physiological stress and environmental toxins. It is a potent trigger of oxidative protein and DNA damage-including DNA strand breakage and base modification. It activates the nuclear enzyme poly-ADP ribose polymerase (PARP) resulting in energy depletion and apoptosis/necrosis of cells. Peroxynitrite generation is a crucial pathological mechanism in stroke, diabetes, inflammation, neurodegeneration, cancer, etc. Peroxynitrite modified DNA may also lead to the generation of autoantibodies in various autoimmune disorders such as systemic lupus erythematosus (SLE). In chronic inflammatory diseases, peroxynitrite formed by phagocytic cells may cause damage to DNA, generating neoepitopes leading to the production of autoantibodies. Hence, understanding the pathophysiology of peroxynitrite could lead to important therapeutic interventions.

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