Synchronize Ovulation Instead of Estrus Synchronizing ovulation rather than estrus would allow producers to mass mate a group of cows without observing them for signs of estrus. Colorado State University researchers have devised an ovulation synchronization protocol called CO-Synch that allows producers to do just that.
The CO-Synch protocol includes an injection of GnRH followed one week later by an injection of PGF (2 alpha). Another injection of GnRH is coupled with timed insemination two days after the PGF (2 alpha) injection. (See Table 1).
This protocol differs from the Ovsynch protocol used in dairy cattle by inseminating cows at the time of the second GnRH injection rather than one day later. Thus, CO-Synch requires one less handling of cattle.
Field trials involving 1,245 beef cows at five locations have demonstrated that pregnancy rates of cows inseminated at the time of the second GnRH injection (54%; CO-Synch) were not different than insemination 24 hours later (58%; Ovsynch). Whereas, a 1996 trial demonstrated that pregnancy rates were higher for cows receiving the Ovsynch protocol (54%) than for cows receiving the Syncro-Mate B protocol (42%).
Another important component of CO-Synch is that it initiates estrous cycles in some cows that have not begun cycling following calving. Forty-eight hour calf removal [from the time of the PGF (2 alpha) injection until the GnRH injection and timed insemination] has increased pregnancy rates from 53% to 62%.
Synchronization of ovulation can be more expensive than synchronization of estrus (costing $9 -10/cow), primarily because of semen costs. With synchronization of ovulation, all cows are inseminated rather than only those cows observed in estrus. However, it should result in more calves born earlier in the calving season and more opportunities for each cow to conceive during the breeding season, resulting in a decrease in the number of replacement females needed.
For more information contact Tom Geary, Colorado State University, 970/491-6244 ([email protected]). n
Electric Prods Deemed OK Penn State researchers say electric prods are useful for moving cattle if used in a controlled manner.
Researchers conducted a study to determine the effects of electric shock, buzzing or touch of a prod on the time required to move weaned beef heifers through a chute system and to determine any negative stress responses animals may exhibit.
Animals that were shocked (1 second/exposure) moved through the chute faster than either the touch only or buzz only groups. Although the shocked animals more frequently exhibited negative behavior responses such as running, kicking or pushing past barriers, the animals' heart rates, respiration rates and temperatures were not different among the three handling methods. Researchers concluded the stress from moving animals through a chute is more stressful to an animal than a short electrical shock.
Researchers advise animals should never be shocked around the head, face or neck, and animals must have room to move forward in the chute. For example, shocking the last animals in a group of bunched cattle is not effective in moving the front animals and causes unnecessary stress to the shocked cattle.
For more information contact Darron Smith, Penn State, at 814/863-6053.
Memory Used In Foraging Decisions Experience and memory appear to play an important role in an animal's foraging locations, says University of California researcher Emilio Laca.
By utilizing their spatial memory, livestock are able to return to high quality foraging sites and achieve a higher foraging efficiency, but this often results in uneven distribution of grazing, Laca says.
To test his theory, Laca exposed six steers to three food distribution treatments for 15-20 min. each day. The treatments included variable-random (food locations were changed randomly and daily), constant-random (food locations were randomly set at the beginning and remained the same throughout the experiment) and constant-clumped (food locations were constant and clumped in groups of five). Pelleted feed was available in 20 of 64 feeders arranged in eight rows and eight columns.
Intake rate increased as animals gained experience, but increased more slowly in variable-random than constant-clumped and constant-random treatments. Time eating per food location decreased with increasing experience. Intake rate was negatively affected by search time per food location, which in turn was determined by the steers' ability to remember food locations.
Steers in constant-random and constant-clumped treatments used long-term spatial memory to return to food locations, and ignored areas where no food was found. Conversely, animals in variable random treatments were unable to use spatial memory and were less efficient, but established a systematic search pattern and utilized most of the available area.
Laca concluded a more uniform grazing pattern may be promoted by impeding spatial memory and preventing animals from developing high expectations of concentrated food rewards in specific locations. This might be accomplished by moving animals from grazing units frequently or by training livestock to expect high rewards such as supplements in unpredictable locations.
For more information contact Emilio Laca, University of California-Davis, 530/754-4083 ([email protected]).
Graze Swaths, Cut Costs High inputs (labor, machinery, etc.) make baled hay one of the highest cost feed sources. Leaving hay in windrows after harvest and allowing cattle to graze the windrows directly can eliminate the costs of baling the hay, moving and stacking bales and feeding bales. (See Table 3.) But how does it affect animal performance?
In 1996 and 1997, Colorado researchers conducted two experiments to determine if cattle performance differs between cattle grazing millet hay stored in windrows compared to eating millet hay stored as small square bales.
Foxtail millet was planted in early June and harvested at the early milk stage in late July and early August. Windrow grazing and bale feeding was conducted from early November to late December.
Crude protein, neutral detergent fiber, acid detergent fiber, cell solubles and total digestible nutrients were tracked.
Overall, leaving millet hay in windrows did result in a loss in forage quality compared to baling and storing hay; however, it was not enough to affect animal performance. Animal performance was similar for the two treatments.
Storing hay in windrows rather than bales can lead to dramatic cost reductions for producers. Based on cost comparisons, a producer could save 43 cents/hd./day in feed costs by allowing cattle to graze windrows, rather than feeding baled hay.
For more information contact Jack Whittier, Colorado State University, at 970/491-6233.
Feed High-Oil Corn For More Marbling A high-oil diet can increase marbling scores, say University of Idaho researchers, resulting in an increased number of carcasses grading USDA Choice and qualifying for Certified Angus Beef premiums.
Sixty Angus-based crossbred yearling steers were used to evaluate the effects of high-oil corn on growth performance and carcass traits in an 84-day finishing trial.
Steers were initially implanted with Synovex-S and adjusted to a high-grain diet over 21 days. Steers were then allotted by weight to one of three treatments: 1) control corn (C; 82% normal corn, 12% silage) 2) high-oil corn (HO; 82% high-oil corn, 12% silage) and 3) high-oil corn formulated to be isocaloric to C (ISO; 74% high-oil corn, 20% silage).
Dry matter intake was greater for steers fed C than HO and ISO diets. Daily gain and feed efficiency were not affected by dietary treatment. However, steers fed both HO and ISO diets tended to have lower average daily gain than steers fed C (4.27 and 4.38 vs. 4.51 lbs./day).
At 72 hours postmortem, carcass data was collected from all carcasses. No treatment differences were observed for hot carcass weight, dressing percent, fat thickness, ribeye area, kidney pelvic and heart fat percent, yield grade and skeletal maturity. Marbling score and quality grades were higher for HO than C. However, marbling scores did not differ between ISO and C. Overall, 78% of HO steers graded Choice, compared to 47% for C and 67% for ISO.
The researchers note that although feeding high-oil corn failed to improve growth performance and efficiency, higher marbling scores would result in an economic advantage when the spread between Choice and Select carcasses is large.
For more information contact Carl Hunt, University of Idaho, at 208/885-6932 ([email protected]du).
Cows should be artificially inseminated about 18 hours after the onset of estrus, Oklahoma State University (OSU) researchers say. This is later than the traditional a.m./p.m. rule.
Pregnancy rates could be increased by 10-20% with artificial insemination by breeding at the proper time, OSU researchers say.
Researchers evaluated 17 Angus x Hereford cows to determine time of ovulation relative to onset of behavioral estrus during August and September. HeatWatch(r) (an electronic sensor that records each time a cow is mounted) was utilized to determine duration of estrus, number of mounts and longest interval between two mounts.
Visual observations were conducted twice daily for 30 minutes at 7 a.m. and 6 p.m., but only identified 13 of 17 cows that were detected in estrus by HeatWatch.
Beginning 16 hours after the onset of estrus, ovaries were evaluated by transrectal ultrasonography every four hours to determine time of ovulation.
The average time from end of estrus to ovulation was 20.6 hours, and duration of estrus averaged 10.8 hours (See Table 2).
The researchers concluded beef cows ovulate an average of 32 hours after the onset of estrus and time of ovulation is not related to the duration of estrus. This indicates that the best time to inseminate is about 18 hours after the onset of estrus, according to OSU researchers.
For more information contact Robert Wettemann, Oklahoma State University, at 405/744-7390 ([email protected]).
Initial body composition plays an important role in a heifer's ability to respond to periods of energy restriction, say University of Minnesota animal scientists.
Females that carry extra condition when exposed to nutritional stress can continue to show estrous cycles longer than more moderate condition females.
Therefore, researchers suggest to prevent females from becoming anestrous, cow-calf operators should not permit any female to reach body condition scores lower than 5. Among heifers a condition score of 6 is probably more adequate.
Twenty pubertal heifers were evaluated to determine the influence of initial body composition (BC) on reproductive response to energy restriction and refeeding. Heifers were randomly assigned to gain or maintain bodyweight (BW) for 57 days to create two distinct body condition score groups: fat (FC; BCS 7.0) or moderate (MC; BCS 5). Then, heifers were fed a low-energy diet (30% NEm) until estrous cycles stopped, and switched to a high-energy diet (65 Mcal NEg/cwt.) ad libitum until estrous cycles resumed.
Body condition scores and BC were determined by visual appraisal at anestrous and cycling.
Females in better condition at the start of nutritional stress did not need to gain as much condition to start showing estrous cycles again. However, regardless of initial body composition, heifers became anestrous at similar BW, BCS and percent empty body fat (PEBF), indicating that anestrous was caused by heifers reaching a certain end-point rather than by losing a certain amount or percentage of weight. That end-point appears to be a body condition score of 3.
Researchers advise managing cows to increase body reserves prior to nutritional stress periods. However, the ability of both groups to respond to re-feeding indicates that these problems, if encountered, can be overcome by feeding high energy diets.
For more information contact Alfredo DiCostanzo, University of Minnesota, at 612/624-1272 ([email protected] umn.edu).
Producers may soon be able to cull cattle that lack the genetic ability to resist parasites, according to USDA researcher Louis Gasbarre.
Gasbarre believes cattle genetics play a major role in determining parasite transmission in a cow herd and the development of immunity in individuals,
Gasbarre says nematode parasites are not "normally" distributed in cattle herds, and after several months on pasture, most cattle show resistance to parasites either by killing incoming worms or by reducing the egg output of worms. However, 15-20% of cattle do not exhibit this resistance.
As a result, these "susceptible" calves are responsible for most of the parasite transmission that takes place on pastures. Gasbarre estimates the heritability of this resistance is approximately 30%. Analyses showed the risk that a certain bull may produce those susceptible, high egg-shedding calves can be as much as 20 times that of another bull.
Current studies are aimed at characterizing the mechanisms that determine immunity and identification of the genes controlling this immunity. To aid producers in breeding decisions, a search is being made to find accurate and economical methods that identify susceptible and resistant cattle. For more information contact Louis Gasbarre, USDA Agricultural Research Center, Beltsville, MD, at 301/504-8509 ([email protected]).
Alfalfa leaf meal (ALM), a by-product of separating alfalfa leaves from stems, can be an effective protein substitute for soybean meal (SBM) in receiving and finishing diets, according to University of Minnesota researchers. The substitution has no detrimental effect on performance, carcass quality or animal health.
Ninety-six medium-frame steers were randomly assigned to one of four dietary treatments for a 167- or 189-day finishing phase. Treatments included control (supplemental protein from SBM) and ALM providing 33%, 66% or 100% of supplemental protein with the balance being SBM.
When feeding ALM, no significant differences were found in kidney, pelvic, heart fat percentage, marbling score, yield or quality grade. Moreover, there was a slight reduction in incidence of liver abscesses in steers that received ALM as the only supplemental protein source.
Steers fed diets containing 100% ALM as supplemental protein or soybean meal-based supplements had heavier carcasses than steers fed 33% or 66% of ALM as supplemental protein. Substituting ALM for SBM increased dry matter intake, but this increase was accompanied by an increase in gain which resulted in similar feed efficiency.
In a similar study with receiving diets, Minnesota researchers concluded substituting ALM for SBM in corn-based diets of receiving steers can be accomplished without a negative effect on animal performance or health. However, feedlot operators using faster fermenting grains in receiving rations should add no more than 33% of ALM as a supplemental protein until more data is gathered.
For more information contact Alfredo DiCostanzo, University of Minnesota, 612/624-1272 ([email protected]).
Speed Up Aging Administering an oral calcium gel to steers three to six hours prior to slaughter results in a shorter postmortem aging time and improved tenderness, says University of Idaho meat scientist Susan Duckett.
Twenty-nine steers were assigned to either a non-dosed control or calcium gel-dosed treatment. Three to six hours prior to slaughter, steers in the calcium gel treatment received 150 g of calcium orally. (This research is still in the experimental phase and not commercially available at this time.)
Hot carcass weights, fat thickness, ribeye area, yield grade, marbling score, quality grade and percent kidney, pelvic and heart fat were similar between treatments.
Steaks from steers that received calcium gel had Warner-Bratzler shear force values 1 kg lower than non-dosed steaks after four to seven days of aging. However, no differences were noted in shear force values at two, 14 or 28 days postmortem.
Packers could implement this technology prior to slaughter, Duckett suggests. Packers would also realize the value, but beef producers and the industry would benefit as well from the increase in customer eating satisfaction.
For more information contact Susan Duckett, University of Idaho, at 208/885-7390 ([email protected] edu).