Long-term impacts of 48-h water and feed deprivation on blood and performance responses of grazing Bos indicus Nellore heifers

The study investigated the effects of 48-h water and feed deprivation on blood and the performance of grazing Nellore (Bos indicus) heifers. Twenty-four Nellore heifers (initial body weight [BW] = 238 ± 10 kg; age = 16 ± 2 mo), were ranked by initial BW and age and randomly assigned to one of the two treatments: (1) grazing animals with free access to pasture, water, and mineral-mix (CON; n = 12), or (2) the same grazing conditions but deprived of pasture, water, and mineral-mix for 48 h (DPR; n = 12). The paddocks consisted of Urochloa brizantha cv. Marandu, using a continuous and fixed stocking rate. The experiment lasted 225 d, with the first 14 d considered as the adaptation period (days -14 to -1) and the subsequent 211 d as the evaluation period (days 0 to 211). From days 0 to 2, treatments were applied by keeping the DPR heifers in pens and reintegrating them into the experimental area after a 48-h water and feed deprivation. Individual full BW was recorded on days -14, -13, -1, before (day 0) and after (day 2) treatment application, and on days 6, 11, 12, 41, 42, 210, and 211. Blood samples were collected in the morning on days 0, 2, 6, 12, and 211. A treatment effect was detected (P < 0.001) for shrink BW from days 0 to 2, which was greater (P < 0.001) in DPR vs. CON heifers. Subsequently, DPR animals were lighter (P < 0.001) compared with CON heifers by the end of the deprivation period (day 2). From days 4 to 211, DPR was lighter (P < 0.001) compared with CON heifers after treatment application and for the entire experimental period. In the first 10 d after treatment application (days 2 to 12), DPR heifers showed a partial compensatory average daily gain (ADG; P < 0.001) compared with CON heifers, while no significant differences were observed in ADG between the treatments from days 12 to 42 and 42 to 211 (P > 0.420). Overall ADG (days 2 to 211) was greater (P < 0.001) for DPR vs. CON heifers. All serum variables, except AST, were higher (P < 0.001) in DPR than in CON heifers on day 2 after treatment application. Our study demonstrates that grazing Nellore heifers subjected to 48-h water and feed deprivation experienced significant alterations in their blood metabolites and BW immediately after the stressful event. Although the deprived heifers partially compensated for their BW loss in the early days post-deprivation, they remained 12 kg lighter than the non-deprived animals throughout the production cycle.

Performance, Intake, Feed Efficiency, and Carcass Characteristics of Young Nellore Heifers under Different Days on Feed in the Feedlot

Two studies evaluated the productive characteristics of young Nellore heifers receiving different days on feed (DOF) to determine the biological slaughter endpoint. In Experiment 1 (Exp. 1), fifty-one Nellore heifers [324 ± 19.3 kg of body weight (BW); 16 ± 1 months] were split into three DOF lengths (45, 75, or 105 days), while in Experiment 2 (Exp. 2), thirty-six Nellore heifers (362 ± 25.5 kg of BW; 18 ± 1 months of age) were split into three DOF lengths (45, 90, or 135 days). In both studies, all animals were distributed in complete randomized blocks according to initial BW and stratified via carcass ultrasound. The diet was supplied ad libitum, allowing 3% of refusals. The point at which the animals achieved 25% of ether extract of shrunk body weight (EE_SBW) was defined as the biological endpoint. Thus, relationships were made between some characteristics obtained in both studies. Positive linear relationships were found between backfat thickness (BFT) vs. EE_SBW (p < 0.001, r = 0.84) and BFT vs. body weight (p < 0.001, r = 0.77). Our results suggest that the biological slaughter endpoint for young Nellore heifers is 6.97 mm of backfat thickness or 402 kg shrunk body weight, corresponding to around 75 DOF.

Progesterone dose during synchronization treatment alters luteinizing hormone receptor and steroidogenic enzyme mRNA abundances in granulosa cells of Nellore heifers

The objective was to investigate effects of progesterone (P₄) dose on abundance of luteinizing hormone receptor (LHCGR), aromatase (CYP19A1), 3β-hydroxysteroid dehydrogenase (HSD3B1), and other steroidogenic mRNA transcripts in granulosa cells from dominant follicles. Nellore heifers were assigned to one of six groups: new, first-use controlled internal drug release device (CIDR1) inserted for 5 days (Large-P₄-dose-D5; n = 7) or 6 days (Large-P₄-dose-D6; n = 8), prostaglandin (PG)F_2α administered on D0 and 1 previously-used CIDR (CIDR3) inserted for 5 days (Small- P₄-dose-D5; n = 8) or 6 days (Small-P₄-dose-D6; n = 8), CIDR1 inserted on D0 and removed plus PGF_2α on D5 (Large-P₄-dose-proestrus (PE); n = 7), and CIDR3 and PGF_2α on D0 and 1, CIDR3 removed plus PGF_2α on D5 (Small-P₄-dose-PE; n = 7). Duration of P₄ treatment (D5 compared to D6) affected abundances of CYP19A1 mRNA transcripts, with there being greater abundances on D6 than D5 (P ≤ 0.05). Heifers treated with the large dose of P₄ had a smaller dominant follicle, less serum and intra-follicular estradiol (E₂) concentrations (P ≤ 0.05) and lesser LHCGR, CYP19A1, and HSD3B1 transcript abundances (P ≤ 0.05). Heifers treated to induce PE had a larger follicle diameter (P = 0.09), greater intra-follicular E₂ concentrations and larger abundances of CYP19A1 mRNA transcript (P ≤ 0.05) than heifers of the D6 group. Overall, treatment with larger doses of P₄ resulted in lesser abundances of LHCGR, HSD3B1, and CYP19A1 mRNA transcripts; thus, potentially leading to development of smaller dominant follicles and lesser E₂ concentrations.

Effect of progesterone concentrations, follicle diameter, timing of artificial insemination, and ovulatory stimulus on pregnancy rate to synchronized artificial insemination in postpubertal Nellore heifers

Two experiments were designed to evaluate the effects of treatments with low versus high serum progesterone (P4) concentrations on factors associated with pregnancy success in postpubertal Nellore heifers submitted to either conventional or fixed timed artificial insemination (FTAI). Heifers were synchronized with a new controlled internal drug release device (CIDR; 1.9 g of P4 [CIDR1]) or a CIDR previously used for 18 days (CIDR3) plus 2 mg of estradiol (E2) benzoate on Day 0 and 12.5 mg of prostaglandin F2α on Day 7. In experiment 1 (n = 723), CIDR were removed on Day 7 or 9 and heifers were inseminated after estrus detection. In experiment 2 (n = 1083), CIDR were all removed on Day 9 and FTAI was performed either 48 hours later in heifers that received E2 cypionate (ECP) on Day 9 (0.5 mg; E48) or 54 or 72 hours later in conjunction with administration of GnRH (100 μg; G54 or G72). Synchronization with CIDR1 resulted in greater serum P4 concentrations and smaller follicle diameters on Days 7 and 9 in both experiments. In experiment 1, treatment with CIDR for 9 days decreased the interval from CIDR removal to estrus (Day 7, 3.76 ± 0.08 days vs. Day 9, 2.90 ± 0.07; P < 0.01) and improved conception (Day 7, 57.1% vs. Day 9, 65.8%; P = 0.05) and pregnancy rates (Day 7, 37.6% vs. Day 9, 45.3%; P = 0.04). In experiment 2, treatment with ECP improved (P < 0.01) the proportion of heifers in estrus (E48, 40.9%(a); G54, 17.1%(c); and G72, 32.0%(b)), but the pregnancy rate was not affected (P = 0.64) by treatments (E48, 38.8%; G54, 35.5%; G72, 37.5%). Synchronization with CIDR3 increased follicle diameter at FTAI (CIDR1, 11.07 ± 0.10 vs. CIDR3, 11.61 ± 0.10 mm; P < 0.01), ovulation rate (CIDR1, 82.8% vs. CIDR3, 88.0%; P < 0.01) and did not affect conception (CIDR1, 42.2 vs. CIDR3, 45.1%; P = 0.38) or pregnancy rates (CIDR1, 34.7 vs. CIDR3, 39.4%; P = 0.11). In conclusion, length of treatment with P4 affected the fertility of heifers bred based on estrus detection. When the heifers were submitted to FTAI protocol, follicle diameter at FTAI (≤10.7 mm, 23.6%; 10.8-15.7 mm, 51.5%; ≥15.8 mm, 30.0%; P < 0.01) was the main factor that affected conception and pregnancy rates.