在配种期饲喂金霉素对母猪繁殖性能的影响

本研究选用４０头母猪进行配种期饲喂金霉素试验，以估价配种期喂金霉素对母猪繁殖性能的影响。结果显示：配种期母猪饲喂含金霉素２００ｍｇ／ｋｇ饲料的日粮增加母猪体重。与对照组相比，配种期（Ｐ＜０．０５）、怀孕１１０天（Ｐ＜０．０１）、产仔后２４小时（Ｐ＜０．０１）、产仔后２１天（Ｐ＜０．０５）和断奶期（Ｐ＜０．０１）母猪体重显著增加；除怀孕增重外，分娩失重和哺乳失重略高（Ｐ＞０．０５）；哺乳期饲料摄入降低（Ｐ＜０．０５）；配种受孕率略高。配种期母猪饲喂金霉素显著提高每窝产仔数（Ｐ＜０．０５），出生时、２１日龄和断奶时存活仔猪数都略高于对照组（Ｐ＞０．０５）。出生时存活仔猪体重、２１日龄仔猪体重都略低于对照组（Ｐ＞０．０５），断奶时仔猪体重略高于对照组。断奶至发情的间隔略长于对照组。结论：配种期母猪饲喂金霉素可提高繁殖性能。     

奶牛早孕诊断乳汁孕酮临界值的确定

随机选择健康荷斯坦母牛６３头，其中发情周期牛５头，配后１８－２４天牛３０头和通过直接确定的怀孕牛２８头，按程序采集末乳乳样。用放射免疫测定法（ＲＬＡ）测定乳汁孕酮（ＭＰ４）浓度。以发情第３天ＭＰ４浓度加上２倍标准差为未孕临界值的土限，以配后１８－２４天怀孕牛ＭＰ４浓度的平均值减去１倍标准差为怀孕临界值的下限。结果表明，奶牛ＭＰ４早孕诊断临界值为：≥７．１９ｎｇ／ｍｌ为怀孕，〈４．７２ｎｇ／ｍｌ为未     

半胱胺对奶牛产奶量及血浆生长抑素、生长激素水平的影响

选用１０ 头处于泌乳中期的荷斯坦牛进行自身对照试验。对照期饲喂基础日粮,试验期在基础日粮中添加半胱胺。每隔５ 天一次,剂量为１００ｍｇ／ｋｇ 体重,共喂３ 次。结果表明,试验期奶牛日产奶量比对照期提高７ ．６ ％ （ 对照期１４ ．５ ±３ ．９ｋｇ／ 头,试验期１５ ．６ ±４ ．３ｋｇ／ 头Ｐ＜ ０ ．０５） ;奶牛采食量无明显变化,试验期饲料转化率比对照期明显提高（ 对照期０ ．３２ ±０ ．０１ ,试验期０ ．３０ ±０ ．０２ ,Ｐ＜ ０ ．０１） ;与对照期相比,试验期奶牛血浆生长抑素（ＳＳ） 水平明显下降（ 对照期１ ．２１ ±０ ．３４ｎｇ／ｍｌ,试验期０ ．１４ ±０ ．０５ｎｇ／ｍｌ,Ｐ（ ＜ ０ ．０１） ,生长激素含量显著提高（ 对照期１ ．３３ ±０ ．２６ｎｇ／ｍｌ,试验期１ ．７７ ±０ ．２９ｎｇ／ｍｌ,Ｐ＜ ０ ．０５） ;半胱胺对牛乳脂率无明显影响（ 对照期２ ．１６ ±０ ．５８ ,试验期２ ．５３ ±０ ．０６） 。以上结果表明,半胱胺能明显提高奶牛产奶量,而抑制体内生长抑素,提高内源性生长激素水平,可能为其主要的作用机制。     

鸡线虫对雏鸡成活率及发育的影响

通过雏鸡人工感染鸡蛔虫和异刺线虫的试验证明，鸡蛔虫、异刺线虫单独或混合感染，对雏鸡的成活率及发育均有程度不同的影响。与不感染对照组相比，感染３００个／只蛔虫卵的雏鸡成活率低１９％（Ｐ＜０．０５），死亡峰期在感染后７～１４天，增重低３０．１％（Ｐ＜０．０１），影响增重峰期为感染后第１～１０和２１～４０天；感染同量异刺线虫卵雏鸡成活率低１０．３％（Ｐ＞０．０５），死亡主因是组织滴虫病，增重低１６．６％（Ｐ＜０．０５），影响增重峰期在感染后第１１～２０天，混合感染减半量的两种虫卵，成活率低１４％（Ｐ＜０．０５），增重低３２．９％（Ｐ＜０．０１），死亡及发育受阻期与单独感染蛔虫卵组相似，但部分鸡死于组织滴虫病；单独感染减半量蛔虫卵，成活率低１７．３％（Ｐ＜０．０５），增重低１０．１％（Ｐ＞０．０５），死亡及影响增重峰期基本在感染后第１～１０天。     

玉米源异麦芽寡糖菌质粉对黄羽肉鸡生长性能和激素分泌的影响

本研究在饲粮中分别添加 ３个不同剂量的玉米源异麦芽寡糖菌质粉（ＩＢＳ）,旨在研究其对黄羽肉鸡生长性能和内源性激素分泌的影响。选择 １日龄黄羽肉鸡 ２７０只,公母各占 １／２,随机分成 ５组。对照 １组饲喂基础饲粮,对照 ２组在基础饲粮中添加 ４．２７ｇ／ｋｇ市售食品级低聚异麦芽寡糖粉,试验 １、２、３组分别在基础饲粮中添加 ６、１２、２４ｇ／ｋｇＩＢＳ。结果表明：１）与对照 １组相比,试验 １、２、３组死亡率分别降低 ３３．３０％、４９．９５％、４９．９５％;１～５２日龄,试验 １、２、３组平均日增重分别提高 ８．８０％（Ｐ＜０．０１）、１１．０２％（Ｐ＜０．０１）、７．８０％（Ｐ＜０．０１）;试验 １、２、３组料重比分别降低 ８．７３％（Ｐ＜０．０５）、９．０９％（Ｐ＜０．０１）、６．９１％（Ｐ＜０．０５）;试验 ２组血清中甲状腺素含量提高 ８．６８％（Ｐ＜０．０５）;试验 ３组血清中胰高血糖素含量降低 ２４．７５％（Ｐ＜０．０５）;在血清胰岛素动态变化过程中,采食后 １ｈ,试验 １组提高 ４０．３１％（Ｐ＜０．０５）,采食后２ｈ,试验 ２组提高 ４０．０９％（Ｐ＜０．０５）;在血清生长激素动态变化过程中,采食后 １ｈ,试验 ３组提高 ３５．１８％（Ｐ＜０．０５）,采食后 ２ｈ,试验 ２、３组分别提高 ４８．２６％（Ｐ＜０．０５）、４２．７２％（Ｐ＜０．０５）;试验 ２、３组血清中生长激素含量总体平均值分别提高 ２３．６５％（Ｐ＜０．０５）、２６．２９％（Ｐ＜０．０５）。２）与对照２组相比,试验２、３组死亡率均降低２４．９７％;１～５２日龄,试验１、２、３组平均日增重分别提高 ６．５７％（Ｐ＜０．０５）、８．７５％（Ｐ＜０．０１）、５．５９％（Ｐ＜０．０５）;在血清胰岛素动态变化过程中,采食后 ２ｈ,试验 ２组提高 ４４．５５％（Ｐ＜０．０５）;在血清生长激素动态变化过程中,采食后 ２ｈ,试验 ２、３组分别提高 ５０．２４％（Ｐ＜０．０５）、４４．６３％（Ｐ＜０．０５）;试验 ３组血清中生长激素含量总体平均值提高 ２３．８０％（Ｐ＜０．０５）。结果提示,黄羽肉鸡饲粮中添加一定剂量的 ＩＢＳ,对其生长性能、激素分泌有促进作用,且在本试验的 ３个剂量中,以添加 １２ｇ／ｋｇＩＢＳ综合效果最佳。     

热应激对奶牛血液生化指标及生产性能的影响

用７２头荷斯坦奶牛研究了夏季热应激对血液生化指标及泌乳性能的影响。结果表明：热应激期奶牛血清中γ－球蛋白含量较非热应激期的冬、春、秋季分别降低３９．５１％（Ｐ＜０．０１），３５．８１％（Ｐ＜０．０１）和１６．４８％（Ｐ＞０．０５）；热应激期奶牛血清中抗坏血酸含量较冬、春、秋季分别降低２６．０３％（Ｐ＜０．０１）、１３．３５％（Ｐ＜０．０５）和１５．０１％（Ｐ＜０．０５）；热应激期奶牛血清钙、钾、钠含量显著降低（Ｐ＜０．０１），但对血清镁含量无显著影响（Ｐ＞０．０５）；热应激期奶牛各泌乳阶段泌乳量均显著低于非热应激期（Ｐ＜０．０１），泌乳前期奶牛对热应激的反应较泌乳中、后期奶牛敏感，产奶量下降幅度较大。     

血小板计数法在奶牛超早期妊娠诊断上的应用

对２０头未孕母牛血小板正常值的测定结果为４９６．５×１０９／Ｌ±６６．５×１０９／Ｌ；对３０头受配母牛进行血小板值变化和最佳血检时间的试验，结果表明，２２头妊娠母牛于配种第７天血小板值明显减少（Ｐ＜０．０１）；而８头未妊娠母牛则无明显变化（Ｐ＞０．０５）。根据妊娠母牛配种前后血小板值差＞１９２．３×１０９／Ｌ为妊娠标准，对３０头受配母牛进行了超早期妊娠诊断试验，经直检妊娠母牛符合率为８６．３６％，空怀母牛符合率为８７．５％，总符合率为８６．６６％（Ｐ＞０．０５）。     

半胱胺对小鹅血浆中β-END和某些激素的影响

选用２４只二月龄的杂交鹅（川白×太湖）,随机分成对照组（１２只）和试验组（１２只）。试验组于日粮中一次性添加半胱胺（１００ｍｇ／ｋｇ·ＢＷ）。处理后第三天从翅静脉采取血样。用ＲＩＡ双抗法测定其中的β－ＥＮＤ、ＩＧＦ－Ｉ和各种激素的含量。结果表明：试验组的ＳＳ含量较对照组低１９．６４％（Ｐ＜０．０５）、而ＧＨ、ＩＧＦ－Ｉ和β－ＥＮＤ含量较对照组分别高５０．００％（Ｐ＜０．０１）、６２．８０％（Ｐ＜０．０１）和４４．５５（Ｐ＜０．０５）;与对照组相比较,试验组的ＴＳＨ低３２．３２％（Ｐ＜０．０５）,Ｔ４下降１４．７２％（Ｐ＞０．０５）,而Ｔ３升高２６．８０％（Ｐ＜０．０１）。以上结果提示：半胱胺可能是通过降低鹅血液中ＳＳ含量,使β－ＥＮＤ、ＩＧＦ－Ｉ、ＧＨ和Ｔ３水平升高,从而促进了鹅的快速生长。     

TDP照射居髎穴治疗奶牛卵巢机能性不孕症的效果

用ＴＤＰ（特定电磁波谱）对卵巢机能性不孕症荷斯坦奶牛的居穴生产进行照射。试验组３１头，对照组２７头。照射结果：试验组牛的发情率、受胎率、发情持续时间和妊娠所需配种数分别为７０．９７％、８６．３６％、３．１４±１．２４天和１．０６±０．３９次，与对照组的１１．１１％、３３．３３％、５．７５±２．４５天和１．８３±０．８６次相比，差异极显著（Ｐ＜０．０１）；照射开始至发情和配孕时间，试验组比对照组分别提前了４３．３７天和４１．８２夫，差异极显著（Ｐ＜０．０１）。     

维生素B_（12）注射液解冻牛的冻精试验

用ＶＢ１２注射液解冻牛的冻精与用０．９％氯化钠溶液、复方氯化钠溶液和２．９％柠檬酸钠溶液解冻牛的冻精进行比较，精子活力提高１６．２３％（Ｐ＜０．０１）、１５．４３％（Ｐ＜０．０１）和１２．６７％（Ｐ＜０．０５）；顶体完整率提高１４．１２％（Ｐ＜０．０１）、１３．０３％（Ｐ＜０．０１）和１１．０７％（Ｐ＜０．０５）；而精子畸形率和精清中ＧＯＴ活性均明显地降低（Ｐ＜０．０５）；精子存活时间延长。试验结果表明，用ＶＢ１２注射液解冻牛的冻精对精子形态结构有保护作用．是一种较理想的解冻液。     

Corpus luteum Function and Pregnancy Outcome in Buffaloes during the Transition Period from Breeding to Non‐Breeding Season

The aim in this study was to investigate corpus luteum function and embryonic loss in buffaloes mated by artificial inseminations (AI) during the transitional period from breeding to non‐breeding season. The study was carried out using 288 multiparous Italian Mediterranean Buffalo cows at 110 ± 4 days in milk. The buffaloes were mated by AI after synchronization of ovulation by the Ovsynch‐TAI protocol 25 days after AI buffaloes underwent trans‐rectal ultrasonography to assess embryonic development. Pregnancy diagnosis was confirmed on Days 45 and 70 after AI by rectal palpation. Buffaloes pregnant on Day 25 but not on Day 45 were considered to have undergone late embryonic mortality (LEM), whilst buffaloes pregnant on Day 45 but not on Day 70 were considered to have undergone foetal mortality (FM). Corpus luteum size and blood flow were determined by real‐time B‐mode/colour‐Doppler on day 10 after AI in 122 buffaloes. The resistive index (RI) and pulsatility index (PI) were recorded at the time. Milk samples were collected on Days 10, 20 and 25 after AI in all inseminated buffaloes for the assay of whey P4 concentrations. Data were analysed by anova . Pregnancy rate on Day 25 after AI was 48.6% (140/288) and declined to 35.4% (102/288) and 30.6% (88/288) by Day 45 and Day 70 respectively. The incidences of LEM and FM were respectively 27.1% (38/140) and 13.7% (14/102). Pregnant buffaloes had greater (p < 0.01) whey concentrations of P4 from Day 20 onwards than buffaloes which showed LEM, whilst P4 in buffaloes that showed FM did not differ from the other two groups on Day 10 and Day 20. Corpus luteum blood flow on Day 10 after AI showed higher RI (p < 0.05) and PI (p = 0.07) values in buffaloes that subsequently were not pregnant on Day 25 compared with pregnant buffaloes. Buffaloes that were not pregnant on Day 45 also had a higher (p = 0.02) RI value on Day 10 than pregnant buffaloes, whilst PI values on Day 10 did not differ for the two groups of buffaloes. It was concluded that blood flow to the corpus luteum on Day 10 after AI influences corpus luteum function as judged by P4 secretion and also embryonic development and attachment in buffaloes.     

Relations between plasma IGF-I concentrations during treatment with CIDR-based or Ovsynch protocol for timed AI and conception in early postpartum Japanese black beef cows

We examined the relations between plasma insulin-like growth factor (IGF) -I concentrations during treatment with CIDR-based or Ovsynch protocol for timed AI and conception and plasma steroid concentrations in early postpartum Japanese Black beef cows. Cows in the control group (Ovsynch; n = 21) underwent Ovsynch protocol (GnRH analogue on Day 0, PGF(2alpha) analogue on Day 7, and GnRH analogue on Day 9), with AI on Day 10, approximately 20 h after the second GnRH treatment. Cows in the Ovsynch+CIDR group (n = 22) received Ovsynch protocol plus a CIDR for 7 days (starting on Day 0). Cows in the further treatment group (EB+CIDR+GnRH; n = 22) received 2 mg of estradiol benzoate (EB) on Day 0 in lieu of the first GnRH treatment, followed by the same treatment as in the Ovsynch+CIDR protocol. Plasma IGF-I concentrations were determined on Days -7, 0, 7, 9 and 17. Conception rates were improved in the CIDR-combined groups (both CIDR-treated groups were combined) relative to Ovsynch group (P < 0.05) for cows with low IGF-I concentrations (<1,000 ng/ml) on Days -7, 0, and 7, but improved conception rate produced by the CIDR-based protocols did not occur in cows with a high IGF-I concentration (> or =1,000 ng/ml). Plasma estradiol-17beta concentrations increased from Day 0 to 7 (P < 0.05) and were unchanged from Day 7 to 9 in the Ovsynch group with low IGF-I concentrations on Day 0, while they were unchanged from Day 0 to 7 and increased from Day 7 to 9 (P < 0.05) in the Ovsynch group with high IGF-I concentrations on Day 0 and in the CIDR-combined group. Plasma progesterone concentrations in the Ovsynch group with low IGF-I concentrations on Day 0 were higher on Day 14 than in the Ovsynch group with high IGF-I concentrations on Day 0 and in the CIDR-combined group (P < 0.05). In conclusion, CIDR-based protocols may improve conception relative to Ovsynch in early postpartum beef cows with lower plasma IGF-I concentrations at the start of the protocols. This improvement is probably due to prevention of premature increases of estradiol-17beta and progesterone concentrations, which occurred in cows with low IGF-I concentrations treated with Ovsynch, by the CIDR treatment.     

Effects of flunixin meglumine and transportation on establishment of pregnancy in beef cows

Objectives of these studies were to determine the effects of flunixin meglumine (FM) administration on early embryonic mortality and circulating PG and cortisol concentrations in transported and non-transported cows. Cows (n = 483) from 3 locations were used to evaluate the effects of transportation and FM approximately 14 d after AI on the establishment of pregnancy and serum concentrations of progesterone, PGF metabolite (PGFM), and cortisol. Treatments were transport (n = 129), transport + FM (n = 128), no transport (n = 130), and no transport + FM (n = 96). Multiparous cows (n = 224) were used at 2 locations, and nulliparous cows (n = 259) were used at 1 location. The no transport + FM treatment was used at only 2 locations. Flunixin meglumine (approximately 1.1 mg/kg of BW; i.m.) was administered before the cows were separated into transportation groups. Transportation included 4 to 6 h of transportation, without calves, via semitractor trailer. Nontransported cows remained penned, with their calves in adjacent pens, during the same period as the transported cows. Blood samples were collected from all cows before and after treatment and, at 2 locations, approximately 3 h after the onset of treatment. Location affected AI pregnancy rate (P < 0.01). Treatment effects, although not significant (P = 0.16), were of a magnitude to be considered practically important. Cows that received transportation + FM tended (P = 0.07) to have greater AI pregnancy rates (74%) than those that did not receive FM (66%), irrespective of transportation. Cortisol concentration was greater (P < 0.05) for transported cows than for nontransported cows. Cows receiving FM had greater (P < 0.05) AI pregnancy rates than non-FM cows (71 vs. 61%, respectively). Cows receiving transportation had lower (P < 0.01) mean PGFM concentrations than nontransported cows (45.4 vs. 54.6 pg/mL, respectively), and cows receiving FM had lower (P < 0.01) mean PGFM concentrations than non-FM cows (39.4 vs. 60.6, respectively). We conclude that transportation of cows approximately 14 d after AI increased serum cortisol concentrations but did not affect AI pregnancy rates. However, treatment of cows with FM increased AI pregnancy rates, irrespective of whether they were transported.     

Comparison of plasma concentrations of estradiol-17β and progesterone, and conception in dairy cows with cystic ovarian diseases between Ovsynch and Ovsynch plus CIDR timed AI protocols

The objectives of this study were 1) to determine the effects of adding a CIDR to the Ovsynch protocol on plasma concentrations of estradiol-17β and progesterone and conception in dairy cows with cystic ovarian diseases and 2) to examine associations among the estradiol-17β and progesterone concentrations and conception. Cows were diagnosed as having cystic ovarian diseases if they were found to have a cystic follicle (diameter ≥25 mm) without a corpus luteum by two palpations per rectum with an interval for 7 to 14 days. They were treated with either the Ovsynch (GnRH on Day 0, PGF(2α) on Day 7 and GnRH on Day 9, with AI on Day 10; n=15) or Ovsynch+CIDR protocol (Ovsynch protocol plus a CIDR from Day 0 to Day 7; n=23). Plasma estradiol-17β concentrations were determined on Days 0, 7 and 9, and plasma progesterone concentrations were determined on Days 0, 7, 9 and 17. The plasma estradiol-17β and progesterone concentrations at all of the days examined and conception rates did not differ significantly between the two timed AI protocols. The progesterone concentrations on Day 17 and conception rates were lower (P<0.05) for cows with low concentrations of estradiol-17β (<2 pg/ml) on Day 9 than for cows with high concentrations of estradiol-17β (≥2 pg/ml). The present study suggests that, in dairy cows with cystic ovarian diseases, addition of a CIDR to the Ovsynch protocol had no remarkable effects on plasma estradiol-17β and progesterone concentrations during and after the treatments or on conception after timed AI. This study indicates that the low plasma estradiol-17β concentration at the second administration of GnRH in the protocols can be a predictor for impaired luteal formation and lower likelihood of pregnancy in dairy cows with cystic ovarian diseases.     

Synchronisation of oestrus and reproductive performance of dairy cows following administration of oestradiol benzoate or gonadotrophin releasing hormone during a synchronised pro-oestrus

OBJECTIVE: To compare the use of gonadotrophin releasing hormone (GnRH) and oestradiol benzoate (ODB) administered following a synchronised pro-oestrus on reproductive performance of lactating dairy cows and the submission rates of non-pregnant cows following resynchronisation. DESIGN: Cohort study. PROCEDURE: Lactating Holstein cows enrolled in a controlled breeding program were first treated with an intravaginal progesterone releasing insert (IVP4) for 8 days, 2.0 mg of ODB intramuscular (i.m.) at device insertion (Day 0), an analogue of PGF2alpha at device removal and either 1.0 mg of ODB i.m., 24 h after device removal (ODB group, n = 242), or 0.25 mg of a GnRH agonist (GnRH group, n = 152) injected i.m. approximately 34 h after device removal. Every cow was artificially inseminated between 49 and 56 h after removal of its insert (Day 10). Cows detected in oestrus 1 day after artificial insemination (AI) that were not detected in oestrus on the previous day were re-inseminated on that day. All cows treated on Day 0 were resynchronised for reinsemination by insertion of a used IVP4 device on Day 23. Oestradiol benzoate at a dose of 1.0 mg was administered i.m. at the time of device insertion. Inserts were removed 8 days later (Day 31) and 1.0 mg of ODB was injected i.m. 24 h later. Those cows detected in oestrus between Days 31 and 35 were artificially inseminated. On Day 46 these cows were resynchronised for a third round of AI by insertion of an IVP4 device, used previously to synchronise cows for the first and second rounds of AI, and administration of 1.0 mg of ODB i.m.. Eight days later inserts were removed. Cows detected in oestrus between Days 54 and 58 were artificially inseminated. Bulls were run with the herd between rounds of AI and removed after 21 weeks of mating. RESULTS: Treatment with ODB or GnRH at the first synchronised pro-oestrus did not significantly alter the reproductive performance over three rounds of AI or over a 21-week breeding period. Treatment also did not alter submission rates at the second round of AI or the proportion of non-pregnant and non-return cows ('phantom' cows) detected and did not result in significant differences in concentrations of progesterone in plasma 10 and 18 days after removal of inserts at the first round of AI. Treatment with GnRH reduced the proportion of cows detected in oestrus at the first round of AI (36.2 vs 97.5%; P < 0.001). CONCLUSION: Administration of GnRH compared to ODB at a synchronised pro-oestrus results in similar reproductive performance. Treatment with GnRH reduced the proportion of cows detected in oestrus following treatment. This may offer advantages to the way AI is managed by enabling insemination at a fixed-time and removing the need for the detection of oestrus.     

Fertility in Dairy Cows After Artificial Insemination Using Sex‐Sorted Sperm or Conventional Semen

The aim of this study was to compare pregnancy per artificial insemination (P/AI) after timed AI with sex‐sorted sperm (SS) or conventional semen (CS) in lactating dairy cows. Cyclic cows (n = 302) were synchronized by Ovsynch and randomly assigned into two groups at the time of AI. Cows with a follicle size between 12 and 18 mm and clear vaginal discharge at the time of AI were inseminated with either frozen‐thawed SS (n = 148) or CS (n = 154) of the same bull. A shallow uterine insemination was performed into the uterine horn ipsilateral to the side of probable impending ovulation. Pregnancy per AI on Day 31 tended (p = 0.09) to be less for SS (31.8%) than CS (40.9%). Similarly, P/AI on Day 62 was less (p = 0.01) for cows inseminated with SS (25.7%) compared with CS (39.0%). The increased difference in fertility between treatments from Days 31 to 62 was caused by the greater (p = 0.02) pregnancy loss for cows receiving SS (19.2%) than CS (4.8%). Cow parity (p = 0.02) and season (p < 0.01) when AI was performed were additional factors affecting fertility. Primiparous cows had greater P/AI than multiparous cows both on Day 31 (41.7% vs 25.0% in SS and 53.0% vs 31.8% in CS groups) and on Day 62 (33.3% vs 20.5% in SS and 48.5% vs 31.8% in CS groups). During the hot season of the year, P/AI on Day 31 was reduced (p = 0.01) in the SS group (19.6%) when compared with the rates during the cool season (38.1%). In conclusion, sex‐sorted sperm produced lower fertility results compared to conventional semen even after using some selection criteria to select most fertile cows.     

Effect of Acute Bull Exposure Around the Time of Artificial Insemination on Serum Oxytocin and Progesterone Concentrations and Pregnancy Rates in Dairy Cows

This study examined the effect of acute bull exposure around the time of artificial insemination (AI) on oxytocin and progesterone concentrations, and pregnancy rates in dairy cows. Ninety six dairy cows, stratified according to parity into primiparous and pluriparous, were divided into three groups; short bull exposure (SBE; 10 min, n = 32), long bull exposure (LBE; 4 h, n = 32) or no bull exposure (NBE; n = 32). On day 45 post‐partum, all cows were treated with PGF2α on three occasions 11–14 days apart to synchronize oestrus. They were submitted to fixed time AI 80 h after the third PGF2α injection. Cows in the SBE and LBE groups were artificially inseminated 5 min after the introduction of the bull. From a subset of cows (n = 6 per group; three primiparous and three pluriparous), blood samples were collected once every 5 min starting 15 min before AI until 15 min after AI and analysed for oxytocin concentrations. Additional blood samples were collected for measurements of progesterone (P4) concentrations once daily for 4 days starting on the day of AI and once every 3 days thereafter until day 22. The effects of bull exposure, time, parity, difficulty of AI, and pregnancy on oxytocin and P4 concentrations were analysed using the mixed linear model procedure. Mean oxytocin concentrations or change in oxytocin concentrations after bull exposure or AI were not different among groups. Pregnancy rates for the NBE, SBE and LBE groups were 55.5%, 33.3% and 44.4%, respectively, and were not different among groups. In conclusion, acute bull exposure around the time of AI did not affect oxytocin and progesterone concentrations and did not improve pregnancy rates in dairy cattle under these farms conditions.     

Administration of human chorionic gonadotropin to suckled beef cows before ovulation synchronization and fixed-time insemination: replacement of gonadotropin-releasing hormone with human chorionic gonadotropin

Two experiments were conducted to evaluate whether hCG administered 7 d before initiating the CO-Synch + controlled internal drug release (CIDR) ovulation synchronization protocol (Exp. 1 and 2), or replacing GnRH with hCG at the time of AI (Exp. 1), would improve fertility to a fixed-time AI (TAI) in suckled beef cows. In addition, the effects of hCG on follicle dynamics, corpus luteum development, and concentrations of progesterone (P4) were evaluated. In Exp. 1, cows were stratified by days postpartum, age, and parity and assigned randomly to a 2 × 2 factorial arrangement of 4 treatments: 1) cows received 100 μg of GnRH at CIDR insertion (d -7) and 25 mg of PGF(2α) at CIDR removal (d 0), followed in 64 to 68 h by a TAI plus a second injection of GnRH at TAI (CG; n = 29); 2) same as CG but the second injection of GnRH at the time of insemination was replaced by hCG (CH; n = 28); 3) same as CG, but cows received hCG 7 d (d -14) before CIDR insertion (HG; n = 28); and 4) same as HG, but cows received hCG 7 d (d -14) before CIDR insertion (HH; n = 29). Pregnancy rates were 52, 41, 59, and 38% for GG, GH, HG, and HH, respectively. Cows receiving hCG (39%) in place of GnRH at TAI tended (P = 0.06) to have poorer pregnancy rates than those receiving GnRH (56%). Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows with concentrations of P4 >1 ng/mL at d -7, increased (P < 0.02) concentration of P4 on d -7, and decreased (P < 0.001) the size of the dominant follicle on d 0 and 3, compared with cows not treated with hCG on d -14. In Exp. 2, cows were stratified based on days postpartum, BCS, breed type, and calf sex and then assigned to the CG (n = 102) or HG (n = 103) treatments. Overall pregnancy rates were 51%, but no differences in pregnancy rates were detected between treatments. Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows cycling on d -7 and increased (P < 0.05) concentrations of P4 on d -7 compared with pre-CO-Synch controls. Therefore, pretreatment induction of ovulation after hCG injection 7 d before initiation of CO-Synch + CIDR protocol failed to enhance pregnancy rates, but replacing GnRH with hCG at the time of AI may reduce pregnancy rates.     

The Induction of a Secondary Corpus Luteum on Day 12 Post‐Ovulation can Delay the Time of Luteolysis in High‐Producing Holstein Cows

Luteolysis before the time of maternal recognition of pregnancy is one cause of low fertility in high‐producing dairy cows. The objective of this study was to assess whether induction of a secondary corpus luteum (CL) late in the luteal phase would delay the time of luteolysis. Twenty high‐producing Holstein cows were synchronized to ovulation (Day 0) with the Ovsynch protocol and received hCG (1500 IU im) on Day 12. Corpora lutea formation (as evaluated by ultrasonography) and plasma P4 concentrations were monitored from Days 4 to 36. hCG treatment induced the formation of one secondary CL (CL2) in 11 of 20 cows (55%) from the dominant follicle (mean diameter: 14.2 ± 0.9 mm) of two‐wave (3/11) and three‐wave (8/11) cycles. The maximal diameter of the CL2 (23.3 ± 1.9 mm) was reached approximately 6 days after hCG treatment and was correlated with its structural lifespan (p < 0.01). Cows that formed a CL2 after hCG had higher mean plasma P4 concentrations on Day 14 (+4.5 ng/ml) and Day 18 (+3.0 ng/ml) compared with cows without CL2 (p < 0.05). The structural regression of CL2 begun approximately 8 days after that of the CL1, and the median time at which the first drop in circulating P4 levels occurred was later in cows that formed a CL2 than in those that did not (Day 26 vs Day 18; p < 0.01). Thus, the induction of a CL2 by hCG on Day 12 might reduce the risk of premature luteolysis in high‐producing dairy cows after insemination.     

Factors affecting the success of resynchronization protocols with or without progesterone supplementation in dairy cows

The objective of this study was to investigate factors that influence the success of resynchronization protocols for bovines with and without progesterone supplementation. Cow synchronized and not found pregnant were randomly assigned to two resynchronization protocols: ovsynch without progesterone (P4) supplementation (n = 66) or with exogenous P4 administered from Days 0 to 7 (n = 67). Progesterone levels were measured on Days 0 and 7 of these protocols as well as 4 and 5 days post-insemination. Progesterone supplementation raised the P4 levels on Day 7 (p < 0.05), but had no overall effect on resynchronization rates (RRs) or pregnancy per artificial insemination (P/AI). However, cows with Body Condition Score (BCS) > 3.5 had increased P/AI values while cows with BCS < 2.75 had decreased P/AI rates after P4 supplementation. Primiparous cows had higher P4 values on Day 7 than pluriparous animals (p = 0.04) and tended to have higher RRs (p = 0.06). Results of this study indicate that progesterone supplementation in resynchronization protocols has minimal effects on outcomes. Parity had an effect on the levels of circulating progesterone at initiation of the protocol, which in turn influenced the RR.