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The objective of this experiment was to determine how source of selenium (Se) affects dairy cow performance, antioxidant status, and apparent absorption and retention. Multiparous Holstein cows (n = 24; 597 ± 49 kg BW) were blocked by days in milk (161 ± 18) and randomly assigned to receive 0.3 mg/kg of either: 1) organic Se (selenized yeast; ORG; Sel-Plex-Alltech); or, 2) inorganic Se (sodium selenite; INO) premix, top dressed and mixed into a ration daily. After an 11-week adaptation period (blood and milk sampled monthly), cows received an intraruminal dose of Se77 (either Se77 yeast or NaSe77O3) followed by a 4-day period of blood and rumen fluid sampling, and total collection of feces, urine, and milk. Data were analyzed using PROC GLIMMIX in SAS with fixed effects of treatment, time, and their interaction, and random effect of block. Daily DMI (23 ± 0.6 kg), milk yield (35 ± 1.2 kg), plasma glutathione peroxidase (64 ± 4.2 U), and serum Se (0.11 ± 0.003 µg/g) were not different between treatments during the adaptation period. Serum Se77 maximum concentration and area under the curve (AUC) were not different between treatments for 72 hours following infusion, but rumen fluid Se77 AUC was higher (P = 0.02) for ORG cows. Apparent absorption (64 ± 1.3%) and retention (44 ± 1.5%) of the Se77 dose did not differ between treatments. The ORG cows had lower urinary excretion (13 vs. 17 ± 0.6%; P < 0.01), higher milk excretion (6 vs. 2 ± 0.3%; P < 0.01), and similar fecal excretion (36 ± 1.3%; P = 0.9) of Se77 compared to INO cows. These results indicate that ORG Se increased Se content of milk and decreased Se excretion in urine, but did not alter performance, antioxidant status, and apparent absorption and retention of Se in mid-lactation cows.

Most milk replacers (MR) contain a higher lactose:fat ratio compared to whole milk, potentially affecting nutrient absorption and use by the calf. This study evaluated how body composition and intestinal development were affected when lactose was replaced with fat in MR. Thirty-four calves (43.3 ± 0.8 kg) were blocked (BW and dam parity), and randomly assigned to a high-lactose (43.8% lactose and 17.1% crude fat) or high-fat (37.9% lactose and 23.4% crude fat) MR. Calves were fed pooled colostrum within 2 h (18% of metabolic body weight (MBW)) and 12 h (9 %MBW) postnatal, followed by MR feeding (18 %MBW) twice daily. Calves were weighed pre-prandially at birth and on d 7. Calves were euthanized on d 7 to sample intestinal tissue and analyze body composition using dual-energy x-ray absorptiometry. Samples of intestinal segments were processed to evaluate histomorphology using bright-field microscopy. Data were analyzed using PROC MIXED in SAS software. Total gain (3.90 vs. 2.29 ± 0.38 kg, P = 0.01) and gain:ME intake (44.64 vs. 28.61 ± 4.32 kg, P = 0.02) were greater for high-fat compared to high-lactose calves, whereas body composition was unaffected (P = 0.13). Proportionally, the large intestine was 0.11 ± 0.02 %BW heavier (P = 0.03) in high-fat calves compared to high-lactose calves, while their small intestine tended to be 0.16 ± 0.06 %BW heavier (P = 0.09). Small and large intestine length did not differ (P = 0.96). High-fat calves had wider villi (125.41 vs. 96.58 µm, P = 0.05) in the jejunum but shorter villi (414.17 vs. 470.96 µm, P = 0.02) in the ileum compared to high-lactose calves. Macronutrient composition affected intestinal histomorphology and improved efficiency of ME use for BW gain. Understanding how fat (including its source) influences nutrient efficiency in dairy calves may improve nutritional strategies on farm.

Inorganic sources of trace minerals are commonly supplemented in dairy cow diets; however, there has been an increase in the supplementation of minerals complexed with organic compounds. These organic trace minerals are thought to have greater bioavailability which may enhance rumen fermentation and absorption. The objective of this study was to assess the effects of dietary concentration and source of supplemental trace minerals on serum trace mineral status and rumen fermentation. Six lactating Holstein cows were used in a 6 x 6 Latin square design with a 23-day adaptation and 5-day experimental period. Cows were fed the same basal diet daily except for the difference in source [organic (ORG) versus inorganic (INO)] and concentration (50%, 100%, and 200% based on NRC recommendations) of trace mineral supplemented. During the experimental period feed intake and blood were collected daily. Rumen fluid was collected on the final two days of the experimental period. Data was analyzed with PROC MIXED in SAS 9.4. Dry matter intake (18.1 ± 0.70 kg), serum mineral concentrations (Cu, Mn, Se, and Zn), and rumen pH (6.5 ± 0.64) did not differ among the treatments. However, serum concentration of Co was higher in 200% ORG compared to 50% and 100% INO and 50% ORG. Ruminal concentration of acetate was higher in 50% and 100% ORG compared to 200% ORG. Butyrate ruminal concentration was higher at 50% ORG compared to 200% ORG. Ruminal propionate concentration was higher in 50% INO and 50% ORG compared to 100% INO and 200% ORG. These findings demonstrate serum trace mineral status and ruminal pH are not tightly controlled by the source of trace minerals when supplemented at 50%, 100% and 200% of the NRC recommendations, however rumen fermentation may be affected by the dietary concentration of trace minerals in the diet.