Slow Release Rbst Administration During the Transition Period on Performance and Blood Cell Counts of Dairy Cows

| This study aimed to evaluate recombinant bovine somatotropin (rbST) supply on feed intake, performance, serum metabolites, and blood cells count of transition cows. Thirty pregnant Holstein cows (607 ± 28.6 kg of body weight) were randomly allocated to one of the following treatments: 1) Control (CON), without rbST supply; and 2) rbST: 250 mg of slow release rbST (Lactotropin, Elanco Animal Health, USA) supplied every 14 d from 28 d of the expected calving date until 28 d of lactation. rbST group had increased dry matter intake during the post partum period and higher body condition score in both preand post-partum periods compared to CON. rbST treatment increased milk yield and milk fat content. Although no effects were observed on serum metabolites before parturition, rbST increased post-partum serum concentrations of glucose, cholesterol, and ionized calcium, and decreased serum concentration of triacyglyceride. rbST had minor effects on complete blood cell count, which included reduced neutrophil counts. In conclusion, this study supports that rbST supply during transition period improves performance of dairy cows that is partially related to improvements in metabolism.


INTRODUCTION
T he transition period of dairy cows is characterized by a sharp decline in dry matter intake (DMI) and negative consequences in animal's health and productivity after parturition (Grummer, 1995). Improved milk production increases energy requirements and results in negative energy balance (NEB), in which cows mobilize energy reserves . Besides high growth hormone (GH) concentration, animals in NEB shows insulin resistance and reduced glucose uptake by peripheral tissues (Bell and Bauman, 1997). Incomplete oxidation of mobilized fatty acids could comprise liver function and predispose animals to ketosis (Grummer et al., 2004). On the other hand, animals that drastically lose body score condition (BCS) during transition period shows are more susceptible to health problems , probably in consequence of an altered structure and function of immune cells.

Advances in Animal and Veterinary Sciences
October 2020 | Volume 8 | Issue 10 | Page 1080 Recombinant bovine somatotropin (rbST) is a synthetically-derived formulation of somatotropin, that has been traditionally used to increase milk production efficiency in dairy cows: rbST increases lactation milk yield by altering the lactation curve (de Morais et al., 2016). Recombinant bovine somatotropin reduces insulin negative effects on gluconeogenesis (Peel and Bauman, 1987) and increases fatty acids oxidation (Pocius and Herbein, 1986). In addition, rbST increases glucose availability for lactogenesis and immunological response. Putnam et al. (1999) found improved DMI, serum glucose concentration, and milk yield of cows treated with 500 mg of rbST every 14 d, in the peripartum. Gohary et al. (2014) evaluated 325 mg of rbST supply every 14 d, and reported increased blood glucose concentration during pre-partum, without major effects on DMI, post-partum diseases incidence, and reproductive performance. Insulin-like factor 1 (IGF-1) stimulates growth, differentiation and functionality of immune cells (Heemskerk et al., 1999). Silva et al. (2017) reported that 125 mg of rbST, every 7 d, from -21 to 28 d relative to calving increased IGF-1 concentration, intensity of phagocytosis, and oxidative burst of polymorphonuclear leukocytes.
Therefore, the hypothesis of the current study was that rbST supply to transition cows would improve DMI, productive performance, serum glucose concentration, and blood leukocyte counts. This study aimed to evaluate the effects rbST supply on milk yield and composition, serum metabolites, and complete blood cell count of transition Holstein cows.

MATERIAL AND METHODS
This study was approved by the Ethics Committee of the Federal University of Grande Dourados. This experiment was carried out in a commercial dairy farm located at Mato Grosso do Sul State -Brazil, between January and August 2016.

manaGemenT, animal, and TreaTmenT
Thirty multiparous and pregnant Holstein cows (607 ± 28.6 kg of body weight -BW) were housed in individual pens (8 × 4 m), 28 d before expected calving date. Then, animals were randomly allocated to one of following treatments: 1) CON, without rbST supply; and 2) rbST, with 250 mg of rbST (Lactotropin ® , Elanco Animal Health, USA), supplied every 14 d until 28 d of lactation. The rBST dose was administered after fractionation of the original 500 mg packaging in half with the aid of sterile syringes. Pre-and post-partum diets were formulated according to NRC (2001) and animals of different experimental groups received the same diets (Table 1). Evaluations were performed weekly until 28 d post-partum. Amounts of feed and orts of each cow were weighed daily and orts were adjusted to 5% to 10% of feed intake as-fed basis.

samPle ColleCTion and CHemiCal analyses
Samples of corn silage were taken weekly (n = 8) and concentrate ingredients were sampled during the preparation of the mixture (n = 8) for chemical analysis. Orts samples (10% of total daily orts) were collected daily from each cow and were combined into a composite sample per week. Feed intake was recorded daily as the difference between feed offered and orts. Samples of corn silage, concentrate, and orts were analyzed for dry matter content (method 930.15, AOAC 2000). Diet ingredients were analyzed for neutral detergent fiber (NDF), acid detergent fiber, and lignin, using heat-stable α-amylase (Van Soest et al., 1991), ash (method 942.05), ether extract (EE; method 920.39), and crude protein (CP; method 984.13) according to AOAC (2000). Non-fiber carbohydrate (NFC) content was estim-

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October 2020 | Volume 8 | Issue 10 | Page 1081

Body CondiTion sCore and Body WeiGHT
Body weights were measured weekly after milking and before the morning feeding, using a livestock scale for large animals (Brete ME 2.80; Coimma ® , Dracena, Brazil). Body condition score was measured weekly using a fivepoint system (1 = emaciated to 5 = obese) according to Wildman et al. (1982).

Plasma meTaBoliTes and red and WHiTe Cells CounTs
Blood samples for plasma metabolites and complete blood cell count were collected weekly, before the morning feeding, by puncture of coccygeal vessels. Blood samples were also collected during the first 24 h after parturition. Samples were collected in 10-mL vacuum tubes for glucose, total cholesterol, triglycerides, total protein, albumin, total calcium, and urea concentrations. After clot formation, samples were centrifuged at 2,000 × g for 15 min, and serum was frozen until analysis, the samples were centrifuged and frozen while still on the farm. Concentrations of plasma metabolites were analyzed using colorimetric kits (Bioclin, Belo Horizonte, Brazil) and readings were performed in a spectrophotometer (Bioplus 2000 IL, Barueri, Brazil). Ionized calcium (IC) was calculated according to (Oetzel, 2004) as: Complete blood cell count was performed within 2 h after blood sampling using a hematologic analyzer (Vet Scan BC-2800 ® , Bio Brasil, São Paulo, Brazil).

sTaTisTiCal analysis
Data were analyzed using PROC MIXED of SAS (version 9.4, version 9.4, SAS Institute Inc., Cary, NC), according to the following model: with a j:i and e ijk ; where Y ijk = dependent variable; μ = overall mean; T i = fixed effect of treatment (i = 1 and 2); a j:i = random effect of animal j within i treatment (j = 1 to 30); W j = fixed effect of week (k = 1 to 4); T×W ik = fixed effect of interaction between treatment and week of evaluation; e ijk = residual error; = Gaussian distribution; = variance associated with animals random effect; = multivariate normal distribution; R = matrix of variance and covariance due to repeated measures. Akaike's method was used to choose R for each variable. Significance was defined at P ≤ 0.05.

RESULTS
There was no treatment and time interaction effect (P ≥ 0.115) on those variables associated with animal's performance (Tables 2 and 3). Animals treated with rbST showed higher (P ≤ 0.008) DMI and BCS than those animals of CON group, in the post-partum (Table 2). Treatment had no effect (P ≥ 0.179) on BW, and increased (P = 0.002) pre-partum BCS. Administration of rbST improved (P ≤ 0.045) milk yield and milk fat content (Table 3). However, there is no treatment effect (P ≥ 0.206) on protein and lactose milk content and daily production.

DISCUSSION
In the present study, slow release rbST increased serum

Advances in Animal and Veterinary Sciences
October 2020 | Volume 8 | Issue 10 | Page 1084 glucose and cholesterol of cows during the post-partum period. Sanchez et al. (2014) reported positive effects of rbST application on serum glucose and cholesterol. The latter authors suggested that higher glucose concentration was likely associated with improved gluconeogenesis and DMI. In addition, Sanchez et al. (2014) reported improved milk yield of animals treated with low doses of rbST during transition period, due to higher efficiency of convert propionate into glucose. Increased serum concentration of glucose and insulin in animals treated with rbST have been observed when samples are obtained during peripartum period (Gohary et al., 2014;Gandra et al.2016).
Besides the positive effects on cholesterol, rbST reduced triglycerides concentration. Fat is mainly stored as triglycerides and transported as free fatty acids bound to albumin. Animals treated with rbST showed higher BSC in both evaluated phases, suggesting a less intense fat mobilization. As observed by Pocius and Herbein (1986), rbST improves fatty acids oxidation and reduces free triglycerides serum concentration, as observed in the present study.
The reduction in triglycerides for cows supplemented with rBST is associated with better BCS, showing less mobilization of body reserves, providing better metabolism of glucose and total cholesterol by the liver, thus increasing milk yield, as well as milk fat content.
rbST increased serum ionized calcium concentration. Eppard et al. (1996) supposed that rbST may have increased bone calcium reabsorption. Cows treated with 500 mg of rbST every 14 d, besides no effect on calcium concentration, observed an increased concentration of hydroxyproline, which is considered a bone reabsorption marker. De Morais et al. (2016) reported positive effect of rbST on milk protein synthesis. This effect seems associated with improved protein synthesis in mammary gland and higher amino acids uptake. However, in the present study, rbST showed no effects on milk protein yield (and content) and serum urea concentration. Reinisch et al. (1996) observed that GH therapy in GH-deficient humans increased release of superoxide anion by neutrophils. In addition, it is well knowledge that insulin-like growth factor (IGF-1) modulates immune cell proliferation (Merimee et al., 1989) and inhibits lymphocytes and neutrophils apoptosis (Baserga et al., 1997).
In the present study, rbST decreased neutrophils count and no others effects were observed on cow's leukogram. However, Silva et al. (2015) supplementing dairy cows with 87.5 or 125 mg of rBST injections were administered every 7 d from −21 to 28 d relative to calving, did not observe any influence of treatments on white cell counts. In addition Silva et al. (2017) using the same dose of rBST in cows in peripartum observed decreased the incidence of uterine disorders in Holstein and Jersey dairy cows and increased yield of ECM during the first 30 DIM, despite slightly increasing the incidence of ketosis.
Besides potential positive effects on immune function, effects could be considered dose-dependent (Gohary et al., 2014). Increasing doses of rbST showed quadratic effect on cytokine production (Zarkesh-Esfahani et al., 2000), and lymphocyte proliferation (Bozzola et al., 1989). Therefore, level of the present study (250 mg) seems higher than optimal dose for optimize immune function. Putnam et al. (1999) observed that injection of somatotropin in the pre-partum period can also lead to increased DMI in the early postpartum period. In the present study, this higher DMI is connected with increased BCS. Previous studies (Putnam et al., 1999;Gulay et al., 2003) reported that cows treated with a low dose of rbST in the peripartum has a better BCS recovery during early lactation, even though they produced more milk.
In the present study, rbST increased 2.4 kg/d (10.7%) milk yield of cows. Additionally, it was observed an 10.8% (3.7 g/kg) increase in milk fat content. Silva et al. (2017) reported greater yields of milk, fat, and energy corrected milk for cows treated with 125 mg of rbST than cows of control. Evaluating late pregnant heifer's treatment with rbST, Schneider et al. (2012) observed 2.8 kg/d increased milk yield during the first seven weeks of lactation. According to Bauman (1992), the main mechanism of rbST effect on milk yield involves increased lipolysis, nutrient prioritization to the mammary gland, and mammary gland epithelial cells proliferation. In general, treatment of pre-partum and periparturient cows with rbST has shown to increase yields of milk and energy corrected milk (Putnam et al., 1999;Gohary et al., 2014).

CONCLUSION
The supply of rbST during transition period improves dairy cows DMI and performance, with positive effects on metabolites concentration and small effects on blood cells count, therefore we recommend using rBST for cows in the transition period