Metabolic and nutritional characteristics of beef cows during pre-calving and lactation periods
Authors:   , Ferreira Matheus Fellipe de Lana 
Published: July 2022

In this thesis, three chapters were prepared based on studies with Nellore cow-calf pairs. Two studies were developed in grazing conditions and a third study was developed in a feedlot facility. In the first chapter, the study aimed to evaluate how metabolic and hormonal traits change over time, their relationship to performance, and determine if these factors differ according to the parity order of grazing beef cows. Thirty-six pregnant Nellore cows (12 nulliparous, 12 primiparous, and 12 multiparous) were used. The study started at 60 d prepartum until 203 d of lactation. The initial body weight (BW) and final BW were higher for multiparous cows (P > 0.05). An interaction occurred between parity and day (P <.0001) for body condition score. Nulliparous and primiparous body condition score were reduced from -60 prepartum to 30 postpartum, then stabilized 60 postpartum (P < 0.05), while multiparous maintained body condition score from -60 days until 60 days postpartum (P > 0.05). Calf BW, final BW, and average daily gain did not differ between parities (P > 0.05). Effect of day (P < 0.05) was detected for non-esterified fatty acids, triglycerides, total cholesterol, LDL, VLDL, progesterone, and insulin. An interaction was observed between parity and days for glucose, HDL, β-hydroxybutyrate, creatinine and IGF-1 (P < 0.05). Parity affected serum urea nitrogen, total proteins, albumin, and globulins (P < 0.05). Parity and day relative to calving did not impact total T3 and T4 (P > 0.05). Hormonal and metabolic profile is strongly influenced by the stage of lactation. Time effects (pre-partum and lactation period) were more pronounced in nulliparous since they displayed more unbalanced metabolic and hormonal traits and lowered BCS pre- and postpartum. In the second chapter, the study aimed to evaluate the effect of parity order on milk yield (MY) and composition over time of grazing beef cows and to evaluate nonlinear models to describe the lactation curve. Thirty-six pregnant Nellore cows (12 nulliparous, 2 years; 12 primiparous, 3 years; and 12 multiparous, 4−6 years) were included in the study. Assigning calving day as day 0, milking was performed using a milking machine to estimate MY on days 7, 14, 21, 42, 63, 91, 119, 154, and 203. Dummy variable analyses were applied to estimate its effects on MY, composition (kg and percentage), afternoon/morning, and afternoon/total proportions. Since multiparous had higher MY than nulliparous and primiparous, two different groups were used for lactation curve analysis: Mult (multiparous) and Null/Prim (nulliparous and primiparous). The MY estimated by the BR-Corte (2016) (Nutrient Requirements of Zebu and Crossbred Cattle) equation was compared with the observed values from this study. Five nonlinear models proposed by Wood (1967) (WD), Jenkins & Ferrell (1984) (JF), Wilmink (1987) (WK), Henriques et al., (2011) (HR) and Cobby & Le Du (1978) (CL) were evaluated. Models were validated using an independent dataset of multiparous and primiparous cows. The estimates for the parameters a, b, and c of the CL equation were compared between groups and the BR- Corte equation using model identity methodology. Nulliparous and primiparous displayed similar MY (P>0.05), however, multiparous cows had an average MY of 0.70 kg/d greater than nulliparous and primiparous (P<0.05). Milk protein and total solids were higher for multiparous cows (P<0.05). Effect of days in milking was found for milk fat, protein, and total solids (P<0.05). The yield of all milk components was higher for multiparous than nulliparous and primiparous. The afternoon/morning and afternoon/total proportion of milk production were not affected by parities and days in milking (P>0.05), with an average of 0.76 and 0.42, respectively. The BR-Corte equation did not estimate correctly MY (P<0.05). The equations of WD, WK, and CL had the best estimative of MY for both Mult and Null/Prim datasets. The equations had very similar Akaike’s information criterion with correction and mean square error of prediction. In the third chapter, the study aimed to measure dry matter intake and digestibility of Nellore cows fed chopped sugarcane or Brachiaria decumbens. grass in the feedlot during the peripartum. Ten pregnant multiparous Nellore cows, with average body weight (BW) of 500±30 was used in this experiment. Cows were randomly divided into two treatments: ad libitum supply of sugarcane and B. decumbens grass. The sugarcane protein content was corrected with urea to reach the protein level of the B. decumbens Cows received a 35% CP supplement during the pre-partum phase in the amount of 1 kg/animal/d and mineral mixed (MM) ad libitum. Cows were fed twice a day (7:00h and 15:00h) and intake was adjusted to allow minimal orts without DMI (dry matter intake) restriction. Intake was calculated by manually weighing the offered feeds and collected orts. The intake measurements started from 24 days before the expected calving date until 24 days postpartum. To evaluate intake and digestibility, a trial was run for 9 days on day 14 before the estimated parturition date and 14 days after parturition. The DMI was similar during pre-partum days except for the parturition that had a decrease of 30% of DMI (P<0.05). During pre-partum, the CP and digestible OM intake were higher (P<0.05) for the sugarcane cows, but apNDF and iNDF intake were higher for B. decumbens cows (P<0.05). An interaction occurred between treatments and day for DMI, in which B. decumbens cows had higher DMI than sugarcane cows after 17 days post-partum (P<0.05). Effect of day was also found, where B. decumbens cows started to increase DMI after 17 days in kg per day and in % of BW. Total DM, OM, CP, apNDF, and iNDF intake were higher for B. decumbens cows during postpartum. Digestibility of DM, OM, and CP was higher for sugarcane cows (P<0.05) at the pre-partum and postpartum period. In summary, the DMI during pre-partum did no change regardless the roughage source, except for a severe decrease at parturition day. The DMI started to increase after 17 days post-partum for the B. decumbens treatment. Keywords: Bos indicus. Gestation. Physiology. Nutrition