The study objectives were to determine the dry matter intake, urine pH, Ca concentration in blood, Ca output in urine, and incidence of hypocalcemia from pregnant, non-lactating dairy cows during the prepartum period consuming diets containing either grass hay (GH) or alfalfa hay (AH) with the inclusion of either calcium chloride (CL) or polyhalite mineral (PO). Eighty Holstein cows in their 2nd parity or greater were fed an experimental diet according to a 2 2 factorial arrangement of treatments during the prepartum period (21 d before calving). All diets had a dietary cation-anion difference (DCAD) below -190 mEq/kg/DM. Grass hay contained 7.5% CP, 74.9% NDF, 0.36% Ca, 0.02% Na, 1.88% K, 0.38% Cl, and 0.15% S. Alfalfa hay contained 19.6% CP, 45.6% NDF, 1.52% Ca, 0.16% Na, 2.5% K, 0.77% Cl, and 0.32% S. Cows consuming grass hay tended to consume more dry matter than cows consuming alfalfa hay (11.6 vs 10.8 kg/d), but dry matter intake (DMI) was not affected by the acidogenic products. Urine pH decreased below 6.5 for all diets and was greatest for cows consuming the GHPO diet. The concentration of calcium in plasma decreased significantly (P < 0.01) around calving but neither the hay type (P=0.86) nor the acidogenic product (P =0.81) affected it. Urinary calcium output was less for cows consuming the GHPO diet. Cows consuming diets containing alfalfa hay had a greater incidence of normocalcemia (37 and 40% for AHCL and AHPO, respectively) than cows consuming diets containing grass hay (20 and 25% for GHCL and GHPO, respectively). In conclusion, alfalfa hay can be included in prepartum diets without necessarily increasing the incidence of hypocalcemia, and the cation-anion difference of alfalfa hay is a determinant of whether it can be included in the prepartum diet. / Master of Science in Life Sciences / Hypocalcemia, low concentrations of calcium in the blood, is more prevalent during the transition from pregnancy to post-pregnancy and can be diagnosed through blood analysis or by observing physical symptoms. The dietary cation-anion difference (DCAD) is the acid-base regulation of the diet and has been used to prevent hypocalcemia during the pre-calving period. The objective of this study was to feed 2 types of hay and 2 types of acidogenic products (Grass Hay/Calcium Chloride, Grass Hay/POlyhalite, Alfalfa Hay/Calcium Chloride, and Alfalfa Hay/POlyhalite) to non-lactating cows in their pre-calving period and observe variables in relation to the incidence of periparturient hypocalcemia. The variables included plasma and urine calcium concentrations pre-calving (21 days) and post-calving (3 days), dry matter intake (DMI) during the pre-calving period, and urine pH. Cows decreased in their dry matter intake toward calving and consumed more grass hay than alfalfa hay (11.6 vs. 10.8 kg/d). All four diets were in a negative DCAD and successfully decreased urine pH for all cows. Calcium concentrations in plasma decreased around calving, but this was not affected by hay type or acidogenic product. Urinary calcium output was greatest in the GHCL-fed cows. The study resulted in further differentiation of cows with plasma calcium concentrations ≤ 5.5 mg/dL without physical symptoms and an animal with ≤ 5.5 mg/dL and a loss of muscle function. Only one cow had a loss of muscle function; however, 13 out of 79 cows had calcium concentrations that according to past research, should've resulted in this. Additionally, 44 out of 79 cows had calcium concentrations between 5.5 and 8.0 mg/dL at least once after calving. In conclusion, alfalfa can be included in pre-calving diets as long as the DCAD is negative.

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In experiment 1, 24 multiparous Holsteins and 24 multiparous Jerseys were assigned at random to one of four diets containing either 1.25, 1.38, 1.50, or 1.63 Mcal NEL/kg DM to determine the effects of prepartum energy density on productivity. Cows were assigned to diets 28 d before expected calving and received a similar diet 0 to 60 d postpartum. Prepartum DMI increased linearly as dietary energy density increased. Non-esterified fatty acids did not differ for energy density and were greater for Holsteins. Milk and 4% FCM increased linearly as dietary energy density increased, although postpartum DMI was quadratic for energy density. Fat yield increased linearly with energy density and protein yield did not differ. Increasing prepartum diet energy density increased yield of milk and 4% FCM. In experiment 2, 26 multiparous and 18 primiparous Jerseys were assigned to one of two CP and rumen undegradable protein (RUP) concentrations 30 d before expected calving to determine the effects of CP and RUP on productivity. Cows received a similar diet 0 to 60 d postpartum. Prepartum CP concentrations were 12 and 15% and prepartum RUP (% of CP) concentrations were 30 and 45%. Dry matter intake was not affected by CP or RUP. Milk yield and 4% FCM yield did not differ for CP or RUP. In addition, milk protein concentration and yield were similar for CP and RUP. Positive calculated metabolizable protein balance for 12% CP and 30% RUP concentrations may have precluded responses to increasing prepartum CP and RUP. In experiment 3, 12 Holstein and 12 Jersey multiparous cows were assigned at random to diets containing 0 or 500 mg FeCO3/kg DM to investigate the effects of dietary Fe on milk production and Cu status. Hepatic Cu did not differ for breeds or Fe supplementation. For Jerseys, hepatic Fe was greater for cows receiving supplemental Fe. Hepatic Zn was similar for breed and Fe supplementation. Plasma Cu was greater for Jerseys compared to Holsteins and did not differ for Fe supplementation. Plasma Fe and Zn did not differ for breeds or Fe supplementation. Iron supplementation did not affect yield of milk or 4% FCM. Dietary Fe did not affect Cu status of Holstein and Jersey cows in this experiment. / Ph. D.

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