Ovulation time in suckled beef cows is anticipated by use of low doses of progesterone and temporary calf removal on fixed timed AI protocol.

This study was designed to evaluate the effect of concentrations of P4 during a fixed-time artificial insemination (TAI) protocol and 48 hours temporary calf removal (CR; i.e., calves were temporally weaned for 48 hours) or treatment with 300 IU of eCG on ovulation time in suckled beef cows. One hundred and fourteen Nellore cows were estrous synchronized by receiving an intravaginal P4 releasing device containing 1.9 g of P4 (CIDR) plus 2.0-mg estradiol benzoate on Day 0, 12.5-mg dinoprost tromethamine on Day 7, and CIDR removal plus 0.5-mg estradiol cypionate on Day 9. Concentrations of P4 (P4 conc.) were manipulated by insertion of a new CIDR containing 1.9 g of P4 (CIDR1) or a CIDR previously used for 9 days (CIDR2), 18 days (CIDR3), or 27 days (CIDR4). On Day 9, within CIDR uses, cows received either CR or eCG. On Day 11 (48 hours after CIDR removal), all cows received a single TAI. Estrus was observed twice, a day between Day 9 and TAI. Ovulation by 60 hours or 72 hours after CIDR removal was defined as the disappearance of the largest follicle (LF) detected on Day 11 and presence of CL on Day 18, determined by transrectal ultrasonography. Cows ovulating after 72 hours were deemed to have a dominant follicle at 60 hours and 72 hours but also had a CL on Day 18. Serum P4 conc. were evaluated on Days 9, 11, and 18. Cows from CIDR4 + CR treatment ovulated at 60 hours (53.3%) tended to be greater (P = 0.07) than CIDR4 + eCG (21.4%). For the remaining treatments, this effect was not detected (CIDR1 + eCG: 6.3% vs. CIDR1 + CR: 0.0%; CIDR2 + eCG: 6.7% vs. CIDR2 + CR: 12.5%; CIDR3 + eCG: 0.0% vs. CIDR3 + CR: 25%). As a consequence, the percentage of cows from CIDR4 + CR treatment ovulating by 72 hours (26.7%) was lesser (P < 0.05) than that of cows in the CIDR4 + eCG treatment (78.6%), but for the remaining CIDR uses ovulation was not affected. The analysis of ovulating time revealed that earlier ovulation was associated (P < 0.01) to: (a) lesser P4 conc. on Day 9 (2.69b, 3.36a, and 3.82a ng/mL, standard error of the mean [SEM]: 0.12); (b) greater LF on Day 11 (12.46a, 12.09a, and 11.06b mm, SEM: 0.34); (c) greater estrus rate (94.1%a, 80.0%a, and 28.6%b), for ovulation at 60 hours, 72 hours, or >72 hours, respectively. Thereafter, previously used CIDR resulted (P < 0.01) in lesser P4 conc. on Day 9 (4.84a, 3.24b, 3.00b, and 2.50c ng/mL, SEM: 0.12), greater LF (10.50b, 12.07a, 11.98a, and 12.33a mm, SEM: 0.18) but only CIDR4 increased (P < 0.05) estrus rate (53.1%b, 65.6%b, 57.9%b, and 90.3%a), for CIDR1, CIDR2, CIDR3, and CIDR4, respectively. In conclusion, cows with low concentrations of P4 during a TAI protocol exhibited increased follicle diameter and an increased rate of estrus. This resulted in a greater percentage of cows ovulating by 60 hours when they had experienced calf removal.

Short communication: Regulation of hepatic gluconeogenic enzymes by dietary glycerol in transition dairy cows.

Nutritional status and glucose precursors are known regulators of gluconeogenic gene expression. Glycerol can replace corn in diets fed to dairy cows and use of glycerol is linked to increased rumen propionate production. The effect of dietary glycerol on the regulation of gluconeogenic enzymes is unknown. The objective of this study was to examine the effect of glycerol on expression of pyruvate carboxylase (PC), cytosolic and mitochondrial phosphoenolpyruvate carboxykinase (PEPCK-C and PEPCK-M), and glucose-6-phosphatase. Twenty-six multiparous Holstein cows were fed either a control diet or a diet where high-moisture corn was replaced by glycerol from -28 through +56 d relative to calving (DRTC). Liver tissue was collected via percutaneous liver biopsy at -28, -14, +1, +14, +28, and +56 DRTC for RNA analysis. Expression of PC mRNA increased 6-fold at +1 and 4-fold at +14 DRTC relative to precalving levels. Dietary glycerol did not alter expression of PC mRNA expression. Expression of PEPCK-C increased 2.5-fold at +14 and 3-fold at +28 DRTC compared with +1 DRTC. Overall, dietary glycerol increased PEPCK-C expression compared with that of cows fed control diets. The ratio of PC to PEPCK-C was increased 6.3-fold at +1 DRTC compared with precalving and tended to be decreased in cows fed glycerol. We detected no effect of diet or DRTC on PEPCK-M or glucose-6-phosphatase mRNA, and there were no interactions of dietary treatment and DRTC for any transcript measured. Substituting corn with glycerol increased the expression of PEPCK-C mRNA during transition to lactation and suggests that dietary energy source alters hepatic expression. The observed increase in PEPCK-C expression with glycerol feeding may indicate regulation of hepatic gene expression by changes in rumen propionate production.

Effect of interval from induction of puberty to initiation of a timed AI protocol on pregnancy rate in Nellore heifers.

Prepubertal Bos indicus heifers (n = 774) were submitted to an E2/P4-based timed artificial insemination (TAI) protocol at three different intervals after induction of their pubertal ovulation by insertion of an intravaginal progesterone (P4) device for 12 days. Heifers were randomly assigned to start the TAI protocol at 10 (group 10; n = 253), 12 (group 12; n = 265), or 14 (group 14; n = 256) days after the P4 device was removed. The TAI protocol consisted of the following: insertion of intravaginal device containing P4 (Controlled internal drug release [CIDR]; previously used twice for 9 days each) + estradiol benzoate (2 mg) on Day 0, CIDR withdrawal + estradiol cypionate (0.5 mg) and PGF2α (12.5 mg) on Day 9, and TAI on Day 11. A subgroup of heifers (n = 472) was evaluated by ultrasound on Days 9 and 11 to evaluate the ovaries and to determine P4 concentrations on Day 9. On Day 9, more (P < 0.05) CLs were present, and follicular diameter was smaller (P < 0.05) for group 10 than for groups 12 and 14 (38.4%, 29.3%, and 23.3% with CL and 9.4 ± 0.1, 9.9 ± 0.1, and 9.8 ± 0.1 mm diameter, respectively), but P4 concentrations did not differ (P > 0.1) between treatments (2.4 ± 0.06 ng/mL). Follicular diameter at TAI (11.08 ± 0.09 mm) and ovulation rate (88.4%) did not differ between treatments (P > 0.1). However, conception and pregnancy rates for all heifers were greater (P < 0.05) in group 12 (50.4% and 45.5%, respectively) than in group 10 (38.2% and 33.7%, respectively), with group 14 intermediate to other treatments (45.6% and 40.6%, respectively). The final pregnancy rate did not differ between treatments (80.9%). In conclusion, a 12-day interval from the end of the puberty induction protocol to the start of the TAI protocol resulted in greater conception and pregnancy rates in prepubertal Nellore heifers.

Frações proteicas do capim-mombaça submetido a doses de nitrogênio em duas alturas de corte / Proteins fractions of mombaça grass submitted to nitrogen doses at two cutting heights

Foram caracterizadas e identificadas as frações proteicas constituintes do capim-mombaça submetido a quatro doses de nitrogênio (0, 100, 300 e 500kg.ha-1) em duas alturas de corte no período chuvoso e no seco. Utilizou-se delineamento experimental em blocos casualizados, em esquema fatorial 4 x 2, com quatro repetições. Os teores de proteína bruta (PB) e das frações A, B1, B2, B3 e C da proteína do capim-mombaça, cortado a 0,20 e 0,40m da superfície do solo foram avaliados pelo Cornell Net Carbohydrate and Protein System. Em relação ao teor de PB, ocorreu diferença significativa (P<0,05) quanto às doses aplicadas. Observou-se aumento de PB em função da elevação das doses de N, principalmente no período chuvoso apresentando valores médios em torno de 10 por cento. Ocorreu diferença nas frações de PB em função da estação e da altura de corte. As frações B1 e C não diferiram quanto à dose de N e altura de corte. As frações A + B1 foram maiores no período seco, nas duas alturas residuais (P<0,05). A dose de nitrogênio e a altura do corte influenciaram na composição das frações proteicas.

The protein fractions of mombaça grass submitted to four nitrogen doses (0, 100, 300, and 500kg.ha-1) at two cutting heights in dry and rainy periods were characterized and identified. A completely randomized block design, in 2x4 factorial scheme with four repetitions, was used. The crude protein (CP) and A, B1, B2, B3, and C protein fractions of mombaça grass cut at 0.20 and 0.40m were evaluated by the Cornell Net Carbohydrate and Protein System. There was significant difference (P<0.05) for CP according to the nitrogen (N) dose. The CP percentage increased as the N dose increased, in rainy period, averaging around 10 percent. There was difference for CP in function of season and cutting heights. The B1 and C fractions did not significantly differ concerning N dose and cutting heights. The A + B1 fractions were higher in the dry period in both heights (P<0.05). The N dose and cutting heights influenced in protein fractions composition.