Protein-energy supplementation on productive and nutritional performance of grazing beef heifers

This study was conducted with the aim of evaluating the effect of protein-energy supplementation on productive performance, intake, digestibility, and microbial protein synthesis in heifers fed tropical forage. Twelve Nellore heifers at 11 months of age, with a mean initial body weight of 248.8 ± 11.40 kg were used. The animals were distributed in a completely randomized design with two treatments and six replicates. The treatments evaluated were: control (without supplementation); and supplementation in the amount of 1.5 kg animal-1 day-1. Forage samples were collected to evaluate the chemical composition and the total availability of dry matter of the pasture consumed by the animals. To evaluate the intake and forage digestibility, a trial was performed using internal and external markers. In this study no effect of supplementation was observed on the intakes of dry matter (DM), organic matter (OM), forage DM, or neutral detergent fiber corrected for ash and protein (NDFap; P > 0.10). However, supplementation increased (P < 0.01) the intakes of crude protein (CP), ether extract (EE), and non-fibrous carbohydrates (NFC). Additionally, an upward trend (P=0.076) was observed in the intake of digested OM (DOM) with supplementation. On the other hand, supplementation increased (P < 0.01) the digestibility coefficients of OM, CP, EE, and NFC, although supplementation did not affect the ruminal synthesis of nitrogen compounds (MICN), efficiency of protein microbial synthesis (EMS), relative microbial nitrogen (RMICN) or urine urea nitrogen (UUN) excretion (P > 0.57). Lastly, supplementation increased (P=0.050) the average daily gain of the animals, although no effect (P > 0.10) was observed on their final body weight. These results suggested that protein-energy supplementation improves the productive performance and nutritional characteristics of grazing beef heifers.

Age at First Gestation in Beef Heifers Affects Fetal and Postnatal Growth, Glucose Metabolism and IGF1 Concentration

This study aimed to determine the effects of age at first gestation on offspring growth performance, glucose metabolism, and IGF1 concentration. Heifers impregnated by AI from a single bull at 15 months of age (15 M, n = 20), or 27 months of age (27 M, n = 20), and multiparous cows (adult, n = 20) were used. Dams from all groups were managed in a single group during gestation and lactation. Gestational length was longer in the 15 M and 27 M than in adult dams (p = 0.009). Bodyweight at birth, at weaning and ADG during lactation were higher in calves from adult dams than in those from 27 M dams, and higher in calves from the latter than in 15 M calves (p < 0.001). Calves from 15 M dams had an increased head circumference/BW ratio compared to calves from 27 M dams, while calves from this latter group had an increased ratio compared to calves from adults (p = 0.005). Body mass index was greater in calves from adults than in those from 15 M and 27 M dams (p = 0.002). Milk production from 15 M and 27 M dams was similar but lower than that from adults (p = 0.03). Calves born from adult dams had greater blood glucose concentrations than those from 15 M and 27 M dams (p < 0.05). Serum IGF1 concentrations were higher in calves from adults than in calves from 15 M and 27 M dams (p = 0.01). This study showed that age at first gestation affects offspring postnatal growth performance, glucose metabolism and IGF1 concentration.

Targeting ADG of Developing Replacement Heifers Using Age and Body Weight

This publication was prepared to assist beef cattle producers and livestock agents in determining the target ADG and management system to develop replacement beef heifers in Florida. Written by John Arthington and Philipe Moriel, and published by the UF/IFAS Department of Animal Sciences, revised October 2021.

PSIII-11 The effect of feeding supplemental zeolite (clinoptilolite) of two different particle sizes on measures of nitrogen utilization and nutrient digestibility in finishing beef heifers

Clinoptilolite (CLN), could potentially improve nitrogen (N) utilization when fed to beef cattle as it can bind ruminal-ammonia-N (NH3-N), limiting its loss and subsequent detoxification into urea-N, which is released into blood and is excreted in urine. However, the effectiveness of CLN is influenced by physical properties such as particle size. Although decreasing the particle size has been shown to increase the binding of ammonium in-vitro, this remains to be evaluated in vivo. Therefore, the objective of this study was to determine the effects of feeding CLN of two different particle sizes (30 and 400 µm) on ruminal NH3-N and plasma-urea-N (PUN) concentrations, ruminal pH, and nutrient intake and apparent total-tract digestibility. Six ruminally-cannulated beef heifers (mean initial BW± SD, 620.8 ± 30.15) were used in a replicated 3 × 3 Latin square design with 21 d periods (sample collection from d 15 to 21). Dietary treatments were: 1) finishing ration with no supplement (CON), 2) CON +30-µm CLN (CL-30), and 3) CON + 400-µm CLN (CL-400). Clinoptilolite was top-dressed (2.5% of diet DM) during morning feeding. Intake was measured daily. Ruminal fluid was collected on d 19 for NH3-N analysis and blood was collected 3 h post-feeding on d 21 for PUN analysis. Indwelling pH loggers were used to measure ruminal pH (d 15 to 21) and grab fecal samples were collected from d 19 to 21 to determine total-tract nutrient digestibility. Statistical analysis was conducted using PROC MIXED in SAS. There was no treatment effect (P ≥ 0.13) on ruminal NH3-N and PUN concentrations, ruminal pH, and nutrient (DM, OM, NDF, ADF and CP) intake and apparent total tract digestibility. In conclusion, feeding CLN to finishing heifers had no effect on measures of N utilization, ruminal pH and nutrient intake and apparent total-tract digestibility.

PSV-4 Peri-estrus ovarian, uterine, and hormonal variables influence the uterine luminal fluid metabolome in beef heifers

In cattle, uterine luminal fluid (ULF) is the main source of molecules that support embryo development and survival during the peri-implantation period. Overarching hypothesis was that peri-estrus changes in ULF volume through accumulation and resorption mechanisms influence ULF composition during the estrous cycle and early pregnancy. Objectives were (1) to characterize individual temporal and spatial changes in ULF volume, endometrial and luteal vascularity, endometrial and luteal size, and progesterone (P4) concentrations during the peri-estrus period in beef heifers and, (2) associate such changes with the metabolite composition in the ULF, four days after estrus. Fourteen Bos indicus heifers that presented a PGF2α responsive CL received 500 µg PGF2α analog i.m. and were examined daily by rectal B-mode and pulse-wave color-Doppler ultrasonography until the fifth day after estrus (estrus = d 0). Plasma P4 was measured daily. On d 4, the uterine body was sampled using a cytology brush for targeted metabolomic analysis by mass spectrometry. Multivariate analyses clustered heifers according to ovarian, uterine, and hormonal variables in clusters A (n = 5) and B (n = 8 heifers). Individual metabolite concentrations were compared between clusters A and B by univariate analysis using t-test after FDR correction. Concentrations of Pro, Ala, Leu, Gly, Val, Lys, Ile, Phe, Asp, Orn, Tyr, Arg, Trp, Suc, Cit, ADMA, the sum of essential Amino Acids (AA), sum of non-essential AA, sum of aromatic AA, and total AA were greater in cluster A (FDR ≤ 0.05). ULF volume dynamics and associated uterine, ovarian, and hormonal variables during the peri-estrus period presented a concerted variation among heifers, which was associated with the ULF composition four days after estrus. Potential implications for embryo receptivity and reproductive outcomes are the focus of the current investigation.

PSIII-10 The effect of a direct-fed microbial (10-G) on live animal performance and carcass characteristics of fed beef heifers

Heifers (n = 1,394; 291 ± 9.9 kg) were used to test the effects of a direct-fed microbial (10-G) on live growth performance and carcass characteristics. Heifers were blocked by arrival day and randomly allocated to treatment (0 or 2g/animal/d; CON and 10-G, respectively) in a randomized complete block design with ten pens per treatment. Heifers were fed for an average of 192 days. Growth and carcass outcomes were analyzed using mixed models with pen as experimental unit and block as random effect. Dry matter intake (P = 0.63), average daily gain (P = 0.69), gain:feed (P = 0.95) and final body weight (P = 0.79) did not differ between treatments. Neither deads and removals (P = 0.52) nor first or second treatment morbidity rates (P ≥ 0.84) were different between treatments. Hot carcass weight (P = 0.19), dressed carcass yield (P = 0.33), 12th rib fat depth (P = 0.73), ribeye area (P = 0.13), calculated empty body fat (P = 0.71) or marbling score (P = 0.20) were not different between treatments. Yield grade distributions did not differ between treatments (P ≥ 0.44), however cattle fed 10-G tended (P = 0.09; 15.78 vs 20.34%) to be represented by fewer USDA Select carcasses. Livers from cattle fed 10-G tended (P = 0.10; 1.02 vs 2.19%) to have a lower frequency of abscesses when compared to CON. Heifers fed 10-G also had fewer (P &lt; 0.05; 5.27 vs 8.51%) severe liver abscesses. These results suggest that supplementing fed beef heifers with 10-G decreased rates of severe liver abscesses without altering live animal performance or carcass characteristics.

PSIII-15 The interactions of change in nutrition after artificial insemination on plasma metabolites, steroid hormones, and uterine histotroph in beef heifers

The objective was to evaluate the impact of nutritional changes after artificial insemination (AI) on plasma metabolites, steroid hormones, and uterine histotroph. Beef heifers (n = 50) were randomly assigned to a post-AI dietary treatment (High=161.5% or Low=77.45% of maintenance energy) until uteri were flushed for embryo recovery (d14). Blood samples were collected on d -3, 0 (AI), 3, 6, 9, 12, and 14 for analysis of plasma non-esterified fatty acid (NEFA), total protein (protein), glucose, cholesterol, and progesterone concentrations. Uterine flushes (UF) were analyzed for concentrations of Mg, P, S, K, Ca, Cu, Zn, Se, Mn, Co, B, Cr, and Fe. Plasma NEFA, protein, glucose, cholesterol, and progesterone concentrations were analyzed as repeated measures in SAS (PROC MIXED). Mineral concentrations in UF were analyzed using the MIXED procedures in SAS. Diet influenced plasma NEFA concentrations, with Low heifers having elevated concentrations (P &lt; 0.01); however, diet did not influence plasma protein, glucose, cholesterol, or progesterone concentrations (P &gt; 0.10). Plasma NEFA, glucose, and progesterone concentrations changed over time (P &lt; 0.05), but protein and cholesterol did not differ over time (P &gt; 0.10). Diet by time interactions influenced plasma NEFA, protein, and cholesterol concentrations (P &lt; 0.05), but glucose and progesterone concentrations were not different (P &gt; 0.10). Presence of a recovered embryo by time interaction influenced plasma protein concentrations (P &lt; 0.04), but NEFA, glucose, cholesterol, and progesterone concentrations were not affected by the interaction (P &gt; 0.10). Embryo recovery and diet by embryo recovery by time did not impact plasma NEFA, protein, glucose, cholesterol and progesterone concentrations (P &gt; 0.10). When an embryo was recovered, Mg (P = 0.02) and S (P = 0.02) were decreased in UF. Diet and diet by embryo recovery did not affect UF mineral concentrations (P&gt;0.10). In conclusion, post-AI nutrition influenced plasma NEFA, protein, glucose, cholesterol, and progesterone concentrations. Additionally, uterine histotroph mineral concentrations were affected by presence of an embryo.

PSIII-26 The effects of maternal melatonin supplementation during pregnancy on longissimus dorsi muscle morphometrics in bovine fetuses at 240 days of gestation

Melatonin is a multifunctional hormone that positively impacts postnatal growth and weaning weight in cattle offspring when supplemented to adequately fed dams during gestation. However, it is unclear whether supplemental melatonin is effective as a countermeasure to decrease effects of a nutritionally compromised pregnancy on fetal tissues. The current study evaluated the efficacy of maternal melatonin supplementation during gestation, as a therapeutic in nutrient restricted beef heifers using fetal LM morphometrics for evaluation of carcass tissue growth. On gestational d 160, 25 Brangus heifers were assigned to one of four groups in a 2 x 2 factorial: nutrient restricted (RES-CON: 60% NRC; n = 6), adequate fed (ADQ-CON; 100% NRC; n = 6), nutrient restricted supplemented with 20 mg melatonin (RES-MEL; n = 7), or adequate fed supplemented with 20 mg melatonin (ADQ-MEL; n = 6). Treatments were top-dressed with 2 mL of melatonin dissolved in 100% ethanol (10 mg/mL) or 2 mL of ethanol (control). At gestational d 240, Caesarean sections and fetal necropsies were performed, both fetal LM were dissected to determine weight, length, and midline circumference. Data were analyzed using the MIXED procedure of SAS. There was a diet by treatment interaction wherein the mass of the left and right LM was increased (P0.035) by an average of 42.46 g in RES-MEL offspring compared to RES-CON fetuses, but no differences (P0.0812) among ADQ groups. Restricted nutrition decreased left LM circumference (10.21 vs. 10.95 cm; P = 0.0445). Treatment had no effect on LM length (P0.1139). In the present study, maternal melatonin supplementation during the Summer promoted muscle growth and mitigated the adverse effects of a nutritionally compromised pregnancy on LM morphometrics. These data are indicative of the potential for melatonin as a gestational therapeutic for prenatal muscle growth and improved efficiency of meat animal production.