The performance of Brahman-Shorthorn and Sahiwal-Shorthorn beef cattle in the dry tropics of northern Queensland. 2. Reproductive rates and liveweights of F2et seq. females

1990 ◽  
Vol 30 (6) ◽  
pp. 727 ◽  
Author(s):  
RG Holroyd ◽  
TA James ◽  
VJ Doogan ◽  
G Fordyce ◽  
R Tyler ◽  
...  
Keyword(s):  
Comparative Analysis ◽  
Beef Cattle ◽  
Pregnancy Rate ◽  
Growth Parameters ◽  
Bos Indicus ◽  
Dry Season ◽  
Lactating Cows ◽  
Dry Tropics ◽  
Percentage Unit ◽  
Reproductive Rates

The female reproductive rates and liveweight performance of F2 et seq. generations of 1/2 Brahman (1/2 B), 1/2 Sahiwal (1/2 Sah), 3/4 Brahman (3/4 B) and 3/4 Sahiwal (3/4 Sah) were evaluated in the dry tropics of northern Queensland from 1978 to 1986. The balance of the breed composition was predominantly Shorthorn. A preliminary comparative analysis of F2 and F3 data showed no differences between the filial generations and data were subsequently pooled. Crossbreed differences between groups had a small effect on pregnancy rate and were not a major determinant of fertility compared with age and year effects. Any crossbreed differences were counteracted by inconsistent cross x year effects. For mature cows, 3/4 Sah had significantly (P<0.05) lower weaning rates than other crosses. The percentage unit difference between pregnancy rate and weaning rate was higher in Sahiwal cross than Brahman cross cows (19 v. 9%). In lactating cows, calving dates were an average 10 days later in 3/4 than 1/2 Bos indicus cows. Generally Brahman crosses were heavier than Sahiwal crosses. In the dry season, Brahman crosses were 16, 30, 36 and 43 kg heavier than Sahiwal crosses for 2-year-old heifers and 3-, 4- and 5-9-year-old cows, respectively. There was little difference between 1/2 and 3/4 B. indicus, except in mature cows, where 1/2 Sah were 27 kg heavier (P<0.05) than 3/4 Sah at start of mating. There were pronounced year effects on all of the reproductive and growth parameters of both heifers and lactating cows. Pregnancy rate and mating liveweight were negatively correlated with date of seasonal break of the dry season (r = -0.71 to -0.88, r = -0.84 to -0.98, respectively). Cross x year interactions for pregnancy rate, calving date and mating liveweight were attributed to factors other than the type of year.

The performance of Brahman-Shorthorn and Sahiwal-Shorthorn beef cattle in the dry tropics of northern Queensland. 1. Reproductive rates and liveweights of F1 and backcross females

1990 ◽  
Vol 30 (6) ◽  
pp. 717 ◽  
Author(s):  
RG Holroyd ◽  
TA James ◽  
VJ Doogan ◽  
G Fordyce ◽  
PK O'Rourke
Keyword(s):  
Beef Cattle ◽  
Bos Indicus ◽  
Research Station ◽  
Data Sets ◽  
Lactating Cows ◽  
Dry Tropics ◽  
Filial Generation ◽  
Sahiwal Cows ◽  
The Difference ◽  
Reproductive Rates

A breeding program was established at Swan's Lagoon Beef Cattle Research Station in the dry tropics of northern Queensland to evaluate the productivity of cattle which were genotypically at least one-half Bos indicus. Brahman or Sahiwal bulls were initially mated to B. taurus cows (predominantly Shorthorn) to produce the first filial generation (F1 1/2 Brahman and F1 1/2 Sahiwal). First backcross 314 Brahman and first backcross 314 Sahiwal were derived from crossing F1 1/2 Brahman or F1 1/2 Sahiwal cows to their respective sire breeds. This paper reports on the female reproductive rates and liveweight performance in 2 data sets: 1972-79, F1 1/2 Brahman v. F1 1/2 Sahiwal; 1975-83, first backcross 3/4 Brahman v. first backcross 3/4 Sahiwal. In both data sets, significant differences in fertility (pregnancy rate and calving date) between F1 or first backcross groups were infrequent, and where differences did occur, they were often inconsistent due to cross x year interactions. The difference between weaning rates and pregnancy rates (representing foetal and calf wastage) was 5 percentage units higher in Sahiwal crosses than Brahman crosses for lactating cows Year effects significantly (P<0.05) influencd both fertility and liveweight, demonstrating the extent of seasonal influences on cattle production in the dry tropics. Generally Brahman-cross cows were heavier throughout than their Sahiwal counterparts. Among lactating cows, F1 1/2 Brahman were 21 kg heavier at start of mating than F1 1/2 Sahiwal, while first backcross 3/4 Brahman were 29 kg heavier than first backcross 3/4 Sahiwal.

Effects of weaning and supplementation on performance of Brahman cross cows and their progeny

1988 ◽  
Vol 28 (1) ◽  
pp. 11 ◽  
Author(s):  
RG Holroyd ◽  
GWJ Mason ◽  
ID Loxton ◽  
PT Knights ◽  
PK O'Rourke
Keyword(s):  
Birth Weight ◽  
Pregnancy Rate ◽  
Management Practices ◽  
Bos Indicus ◽  
Mortality Rates ◽  
Dry Season ◽  
Early Weaning ◽  
Monoammonium Phosphate ◽  
Dry Tropics ◽  
Native Pastures

In a 3-year study in the dry tropics, 2 management practices of dry season supplementation of cows and early weaning of calves were concurrently examined as possible techniques for improving reproductive, liveweight and survival performance of Brahman cross cows (phenotypically 1/2 - 3/4 Bos indicus) grazing native pastures. Cows were either supplemented with a drylick mixture of salt, urea and sulfur (DL) commencing in July for 4-6 months; supplemented with a crisis mixture of salt, urea, grain, molasses, meatmeal and monoammonium phosphate (CM) in the latter part of the dry season; or were not supplemented (C). Mating commenced in January, and calves were either early weaned (EW) at the end of mating in April (mean age of 5 months) or late weaned (LW) in July (mean age of 8 months). Supplements and weaning treatments had little effect on cow liveweight, except between early weaning and late weaning when EW cows gained more or lost less weight (mean advantage of 30.8 kg) than LW cows and were heavier (mean advantage of 44.8 kg) than LW cows at late weaning time. Across all years, 1.4, 2.1 and 4.2% of cows in DL, CM and C groups respectively died from malnutrition or required survival feeding; whereas, in the second and third years, mortality rates due to malnutrition were 0.7 and 2.1% in EW and LW groups respectively. Neither supplement nor weaning treatments had any significant effect on lactating cow pregnancy rates, although data pooled across treatments showed that liveweights at various stages pre-mating were correlated with pregnancy rate. Supplementation or weaning treatments did not influence calving date or birth weight, but LW calves grew significantly faster (mean advantage of 0.52 kg/day) between early weaning and late weaning and were significantly heavier (mean advantage of 57.4 kg) at late weaning than EW calves.

Nutrition of beef breeder cows in the dry tropics. 1. Effects of nitrogen supplementation and weaning on breeder performance

2011 ◽  
Vol 51 (6) ◽  
pp. 515 ◽  
Author(s):  
R. M. Dixon ◽  
C. Playford ◽  
D. B. Coates
Keyword(s):  
Near Infrared ◽  
Body Condition Score ◽  
Management Strategies ◽  
Bos Indicus ◽  
Dry Season ◽  
The Body ◽  
Wet Season ◽  
Lactating Cows ◽  
Dry Tropics ◽  
Body Reserves

The effects of two dry season management strategies consisting of timing of weaning and/or nitrogen (N) supplementation on the body reserves, nutritional status and reproductive performance were, commencing in the early dry season, examined in Bos indicus × Bos taurus breeder cows (n = 122) grazing native pasture in the seasonally dry tropics. Cows were early-weaned in April in the early dry season or late-weaned in September in the late dry season. The supplement consisted of loose mineral mix which provided on average 14 g N/day, principally as non-protein N. In the early dry season in April 1997 all of the cows had been lactating for 3–5 months, averaged 363 kg (s.d. = 28) conceptus-free liveweight (CF.LW) and 4.7 (s.d. = 0.6) body condition score (9-point scale), and 53% were pregnant. In addition, from April to June 1997 10/26 non-pregnant lactating cows, and 24/31 non-pregnant non-lactating (i.e. early-weaned) cows became pregnant so that 81% of cows were pregnant by June. Predictions of diet from near-infrared spectroscopy of faeces indicated that the forage diet selected during the dry season (April–November) by the cows contained on average 9% (s.d. = 2) non-grass dicotyledonous plants and 4.4% (s.d. = 0.38) crude protein (CP), while DM digestibility was 51.1% (s.d. = 1.3). The diet CP concentration, the ratio of CP to metabolisable energy (ME) in the diet (mean 5.7, s.d. = 0.53, g CP/MJ ME) and faecal N concentration (mean 1.05, s.d. = 0.097, % N) all indicated that unsupplemented cows were deficient in dietary N during the dry season. Microbial CP synthesis in unsupplemented non-lactating cows decreased from 360 to 107 g microbial CP/day, or from 6.5 to 2.4 g microbial CP/MJ ME intake, as the dry season progressed from May to September 1997. Net endogenous N transfer to the rumen of up to 2 g CP/MJ ME apparently occurred from May to August. Microbial CP synthesis was 25% higher (P < 0.001) in lactating than in non-lactating cows. From April to September cow CF.LW was improved by 0.35 kg/day (P < 0.001) by early weaning, and by 0.11 kg/day (P < 0.10) by N supplementation, but there was no interaction (P > 0.10) between these treatments. From April to June 1997 calf LW gain averaged 0.79 kg/day, but from June to September was only 0.10 kg/day in unsupplemented paddocks and 0.13 kg/day in N-supplemented paddocks. Pregnant cows calved from November 1997 to March 1998. During subsequent mating 96% of non-lactating cows, but only 17% of lactating cows became pregnant. During the 1997–98 wet season there was compensatory LW gain of lower CF.LW non-lactating cows but not of lactating cows. In conclusion, weaning early in the dry season had a much greater effect than a non-protein N-based supplement to conserve breeder cow body reserves, and the effects of the two management strategies were additive.

Nutrition of beef breeder cows in the dry tropics. 2. Effects of time of weaning and diet quality on breeder performance

2011 ◽  
Vol 51 (6) ◽  
pp. 529 ◽  
Author(s):  
R. M. Dixon ◽  
C. Playford ◽  
D. B. Coates
Keyword(s):  
Diet Quality ◽  
Body Condition Score ◽  
Dry Season ◽  
Near Infrared Reflectance ◽  
Lactating Cows ◽  
Dry Tropics ◽  
Body Reserves ◽  
Wide Range ◽  
Native Pasture ◽  
The Difference

In the seasonally dry tropics the effects of three times of weaning and three nutritional regimes on the changes in liveweight (LW) and body condition score (BCS) of grazing Bos indicus × Bos taurus breeder cows (n = 210) and their calves were examined through an annual cycle, commencing in the early dry season in April 1998. Most of the cows (n = 180) were lactating initially, and were weaned in April (W1), July (W2) or September (W3) to represent the expected early, mid and late dry season. In addition, cows that had not lactated for 11 months before the experiment commenced (NOCALF treatment; n = 30) were examined. The seasonal break occurred in late August, 3.5 months earlier than average for the site. The nutritional regimes consisted of a native pasture (LOW), another native pasture augmented with Stylosanthes spp. legumes (MEDIUM), or this latter pasture supplemented during the dry season with molasses-urea (HIGH). These nutritional regimes were imposed from the commencement of the experiment in April 1998 until February 1999, except that for the HIGH treatment the supplement was fed only during the dry season. Near-infrared reflectance spectroscopy of faeces (F.NIRS) was used to estimate the contents of non-grass, crude protein (CP) and DM digestibility of the diet selected, and also DM intake and metabolisable energy (ME) intake. Diet quality was in accord with the expected seasonal cycle, and was consistently lower (P < 0.05) for the LOW than for the MEDIUM treatment. Concentrations of CP and CP/MJ ME in the diet, and of N in faeces, indicated that the cows grazing the LOW treatment were deficient in rumen degradable protein during the dry season. There was no interaction (P > 0.05) between the nutritional regime and the time of weaning on changes in conceptus-free liveweight (CF.LW) or BCS during the dry season. Weaning increased breeder CF.LW, relative to lactating breeders, by 0.42 kg/day in the early dry season (April–July; the difference between the W1 and W2 treatments), and 0.18 kg/day in the usual mid dry season (July–September; the difference between the W2 and W3 treatments). The NOCALF treatment cows were initially 79 kg heavier than lactating cows, and lost more LW during the dry season. Microbial CP synthesis was 21 and 29% greater (P < 0.05) in lactating than in non-lactating cows in the late dry season and shortly after the seasonal break (August and September), respectively. Calf growth was not affected (P > 0.05) by nutritional regime during the early dry season (April–July), but was lower for the LOW nutritional regime during the usual mid dry season (July–September); this indicated that the LOW nutritional regime cows mobilised sufficient additional body reserves to maintain milk production during the former, but not the latter, interval. All cows that were lactating at the commencement of the experiment gained CF.LW rapidly from September 1998 following the seasonal break. In conclusion, although nutrition affected LW change of both cows and calves, there was a much larger effect of weaning than of the nutrition treatments examined on conservation of body reserves in breeder cows during the dry season. The observation that the effects of weaning on conservation of cow body reserves were similar across a wide range of nutrition is important for management to achieve appropriate targets for breeder cow body reserves.

Effect of cattle tick (Boophilus microplus) infestation on performance of Bos indicus cross cows and their progeny

1988 ◽  
Vol 28 (1) ◽  
pp. 1 ◽  
Author(s):  
RG Holroyd ◽  
PJ Dunster ◽  
PK O'Rourke
Keyword(s):  
Pregnancy Rate ◽  
Bos Indicus ◽  
Treated Group ◽  
Pregnancy Rates ◽  
Boophilus Microplus ◽  
Cattle Tick ◽  
First Year ◽  
The Third ◽  
Lactating Cows ◽  
Tick Counts

The effects of cattle tick infestations on liveweight and fertility of Droughtmaster (1/2 Bos indicus) cows and on calf weaning weights were determined over 3 years. Tick populations on the control (non-dipped) group of cattle fluctuated, with mean annual tick counts/side being 9.5, 8.9 and 13.6 for years 1, 2 and 3 respectively, while the treated group of cattle, which were dipped every 21 days, were free of ticks. Tick counts were not related to fertility or liveweight change in pregnant-lactating cows or to calf growtb or weaning weights. Treatment for ticks significantly (P<0.05) affected liveweight change in pregnant-lactating cows on only a few occasions, and annual liveweight changes were not significantly influenced by treatment. When lactating cow pregnancy rates were low (< 30% for control cows), treatment for ticks increased the pregnancy rate by about 100% in 2 of the 3 years, these differences being significant only in the last year. Calves in the treated group were born significantly earlier in the first year and had significantly lighter birth weights in the third year. Treated calves grew faster to weaning and had higher weaning weights (mean difference 17.9 kg) than control calves but differences were significant in the first and third years only.

Effect of pasture type and supplementary feeding on the reproductive performance of cattle in the dry tropics of north Queensland

1977 ◽  
Vol 17 (85) ◽  
pp. 197 ◽  
Author(s):  
RG Holroyd ◽  
PJ Allan ◽  
PK O'Rourke
Keyword(s):  
Reproductive Performance ◽  
Dry Season ◽  
Conception Rate ◽  
Wet Season ◽  
Lactating Cows ◽  
Dry Tropics ◽  
Stylosanthes Humilis ◽  
Native Pasture ◽  
Conception Rates ◽  
Townsville Stylo

A study was made over a four year period ( 1970-1 973) on the reproductive performance of cows grazing either native pasture stocked at 1 breeder 4.9 ha-1 or native pasture oversown with Townsville stylo (Stylosanthes humilis) and fertilized with superphosphate, stocked at 1 breeder 2.4 ha-1. Animals were supplemented on each pasture type with combinations of molasses, urea and phosphorus at various times of the year. Mating from September 1 to January 31 resulted in animals lactating during the dry season. At double the stocking rate, lactating cows on fertilized pastures had similar conception rates to those on native pasture. During a prolonged dry season, lactating cows on fertilized pasture had twice the conception rate and fewer required survival feeding. Urea compared with non-urea based supplements produced significant increases in conception rates of cows grazing native pasture especially during a dry year. Calves were born earlier, had shorter intercalving intervals and fewer cows had to be fed a survival ration when urea was available. On fertilized pasture, urea based supplements caused only a marginal increase in conception rate except in a dry year, when there was a significant increase. Over the four years, there was a diminishing response in the conception rate of lactating cows grazing native pasture and supplemented with phosphorus during the wet season compared with the control. On fertilized pasture, there was a variable but non-significant response. The addition of phosphorus either as a wet or dry season supplement to urea caused variable responses on each pasture type, but none differed significantly from that of urea.

Effects of different weaning strategies on postweaning growth rate, mortality and fertility of Bos indicus cross cattle

1990 ◽  
Vol 30 (1) ◽  
pp. 1 ◽  
Author(s):  
RG Holroyd ◽  
PK O'Rourke ◽  
R Tyler ◽  
HP Stephenson ◽  
GWJ Mason ◽  
...  
Keyword(s):  
Growth Rate ◽  
Bos Indicus ◽  
Dry Season ◽  
Subsequent Growth ◽  
Wet Season ◽  
Lower Growth ◽  
Treatment Groups ◽  
Pooled Data ◽  
Dry Tropics ◽  
Native Pastures

Three drafts of Brahman cross calves (phenotypically half to three-quarters Bos indicus) were either early weaned (EW) in April (mean age 5 months) or late weaned (LW) in July (mean age of 8 months). Their postweaning performance on native pastures in the dry tropics of North Queensland was monitored through to 2.5 years of age for females and 3.5 years for males. At late weaning, LW calves of both sexes were significantly (P<0.01) heavier than EW calves. Mean liveweight differences over the 3 drafts were 53.8 kg for males and 54.4 kg for females. From late weaning until final liveweight, EW animals partially compensated in growth and were on average 13.6 kg lighter at 3.5 years for males and 20.3 kg lighter at 2.5 years for females than LW animals. In draft 2, pregnancy rate at 2.5 years favoured LW heifers (P<0.05) by 38% units. Mortalities occurred only in the first dry season postweaning with 0, 5 (11.1%) and 5 (8.9%) deaths from poverty in the EW group in drafts 1 to '3 respectively but none in the LW group. Pooled data across treatment groups showed that older calves at weaning had lower growth rates during the first dry season but still had heavier final liveweights. Age at weaning did not influence subsequent growth rate in the first wet season or males in year 2 or year 3 postweaning.

Factors affecting mature size and dry-season weight loss in Bos indicus cross cows in northern Queensland

1988 ◽  
Vol 39 (6) ◽  
pp. 1169 ◽  
Author(s):  
G Fordyce ◽  
S Saithanoo ◽  
ME Goddard
Keyword(s):  
Growth Rate ◽  
Weight Loss ◽  
Adult Height ◽  
Bos Indicus ◽  
Dry Season ◽  
Factors Affecting ◽  
Weight Growth ◽  
Dry Tropics ◽  
Condition Score ◽  
Mature Size

Mature size and dry season weight loss affect the feed requirements, mortality rate and fertility of cows in the dry tropics. The aim of the work reported here was to study the effects of genotype and selection for growth rate on these parameters. The data consisted of: growth rate to 18 months; weight, height and condition score of cows over 5 years old; the change in these parameters during the dry season; and the past fertility of these cows. The cows were + or + bred Brahman of Sahiwal crosses. The Brahman crosses had the same growth rate but a higher mature weight than the Sahiwal crosses. The +-breds lost less weight during the dry season than the +-breds, implying a lower maintenance requirement. Growth rate to 18 monthswas correlated with adult height (r = 0.54) and weight (r = 0.58-0.68). Growth rate was correlated with dry season weight loss (r = 0.36), but only because weight loss was correlated with weight at the start of the dry season. After correcting for this starting weight, growth rate was not correlated with weight loss, and in fact growth rate was positively correlated with condition score late in the dry season (r = 0.17). Adult height was weekly correlated with dry season weight loss (r = 0.13). Past fertility was correlated with current fertility and with ability to maintain condition during the dry season.

The relationships between liveweight, growth from weaning to mating and conception rate of Bos indicus cross heifers in the dry tropics of north Queensland

1991 ◽  
Vol 31 (2) ◽  
pp. 139 ◽  
Author(s):  
VJ Doogan ◽  
G Fordyce ◽  
RK Shepherd ◽  
TA James ◽  
RG Holroyd
Keyword(s):  
Growth Rate ◽  
Growth Rates ◽  
Bos Taurus ◽  
Bos Indicus ◽  
Cohort Effect ◽  
Dry Season ◽  
Conception Rate ◽  
Dry Tropics ◽  
Factors Influencing ◽  
Conception Rates

Factors influencing the conception rates of 1332 Bos indicus cross maiden heifers in the dry tropics of North Queensland were studied between 1973 and 1986. The heifers, which were 112 and 314 Bos indicus (Brahman or Sahiwal) crosses with Bos taurus, were mated at 24-27 months of age over a 3-month period commencing in mid to late January. The effects of liveweights and growth rates on conception rate were initially assessed in separate models which always included cohort (year of branding group) as an additional factor. Cohort and liveweight at weaning, 18 months of age or the start of mating significantly (P<0.05) affected conception rate in maiden heifers. Response to liveweight was curvilinear, being marked for liveweights up to 125-150 kg at weaning, 200-225 kg at 18 months of age and 225-250 kg at the start of mating, with reduced response for greater liveweights. Liveweights of about 270 kg were indicated as targets at the start of mating in a typical year to achieve an 80% conception rate. Average daily gains during the post-weaning dry season and the dry season prior to mating did not influence conception rates after adjusting for cohort. Further analyses using models incorporating both liveweight and growth rate with and without the cohort effect gave indications that the significant cohort effect on conception rate was partly related to post-weaning dry season growth rate. F2 et seq. maiden heifers with low liveweights at either 18 months of age or mating had appreciably higher conception rates if they had gained weight in the post-weaning dry season, rather than losing weight.

15 INCREASING ESTRUS DETECTION RATES WITHIN FOUR DAYS IN A PROSTAGLANDIN-BASED ESTRUS SYNCHRONIZATION PROGRAM IN BOS INDICUS BEEF (SISTANI) CATTLE

2006 ◽  
Vol 18 (2) ◽  
pp. 116
Author(s):  
M. D. Jalinous ◽  
A. Niasari-Naslaji ◽  
F. Sarhaddi ◽  
E. Naghzali
Keyword(s):  
Beef Cattle ◽  
Bos Indicus ◽  
Second Phase ◽  
Estrus Synchronization ◽  
Detection Rates ◽  
Lactating Cows ◽  
Conception Rates ◽  
Group 2 ◽  
Two Phases ◽  
Group 1

Variation in estrous response is a major concern in estrus synchronization programs using prostaglandin F2�. The objective of this study was to confine estrous detection within two phases (48 h each) after synchronizing follicular wave emergence using ovarian follicle regressing (first phase) and ovulating (second phase) agents. Cyclic Sistani cattle (Iranian Bos indicus beef breed) at unknown stages of the estrous cycle and e58 days open were randomly assigned to two groups in mid summer. Females received a ration comprised of wheat straw (39%), Lucerne hay (28%) and concentrate (33%) that comprised 10% crude protein and energy at 2.1 Mcal/kg DM, according to NRC recommendations for beef cattle. In phase one, females in Group 1 (n = 33; heifers: 9; lactating cows: 4; dry cows: 20; 59 � 5.8 months of age; 361.2 � 11.5 kg LW; and 2.1 � 0.41 lactations) received estradiol benzoate (2 mg, i.m., Aburaihan Pharmaceutical Co., Tehran, Iran) and progesterone (100 mg, i.m., Aburaihan, Iran) followed by an injection of prostaglandin analogue (15 mg, i.m., Prosolvin; Intervet, Boxmeer, The Netherlands) and PMSG (400 IU, i.m., Folligon; Intervet) on Day 8. Females in Group 2 (n = 35; heifers: 9; lactating cows: 5; dry cows: 21; 59.3 � 5.7 months of age; 356.8 � 11.5 kg LW; and 2 � 0.35 lactations) received two consecutive injections of prostaglandin 14 days apart. In the second phase, starting 72 h after prostaglandin injection, females in both groups that did not exhibit estrus were given an intra-muscular injection of Gonadorelin (100 �g, Fertagyl, Intervet) followed by prostaglandin injection 7 days later. In both phases, standing estrus was recorded for 48 h, after prostaglandin injection, at 4-h intervals, 30 min each time. Within a defined period (48 h after prostaglandin injection) 12 h after standing estrus, females were inseminated with frozen semen. Pregnancy was diagnosed on Day 30 after insemination using ultrasonography. Data were analyzed using logistic regression and chi-square tests. There was no significant effect of parity and lactation status on the frequency of estrus and conception rates (P > 0.05). The total frequency of observed standing estrus throughout two phases for Group 1 and two females were 81.8% and 80%, respectively (P > 0.05). The conception rates from a single AI for Group 1 [1st phase: 70.6% (12/17); 2nd phase: 40% (4/10); total: 59.2% (16/27)] did not differ (P > 0.05) to that for Group 2 [1st phase: 66.7% (8/12); 2nd phase: 56.2% (9/16); total: 60.7% (17/28)]. The result of this study demonstrated that estrous detection rates of e80% can be achieved within 4 day observation period in Bos indicus beef cattle. The authors express their great appreciations to the Intervet Company, Holland and the Aburaihan Company, Iran, for kind provision of pharmaceutical materials to perform this experiment.

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