146 ■ ANGUSJournal ■ November 2007

Dale ZoBell, Utah State Universityprofessor and Extension beef

specialist, says today’s livestock nutritionistsare faced with a dilemma when it comes toresearching the role minerals play in thewell-being of beef cattle.

“The problem with any mineral study isthat there are so many interrelationships,” hesays. “It is really difficult to attribute a resultto a single cause.”

He adds that this impediment applies toevery aspect of mineral research, includingreproduction.

The scarcity of published studies on theeffects of supplementation on conceptionrates in beef cows doesn’t mean minerals areany less relevant to the reproductive process.Producers should understand thateconomizing on the most important ofthese supplements could affect their bottomline.

This is becoming increasingly evident as agrowing number of scientists respond to thechallenge and develop research models thateffectively isolate the effects of specificminerals on cattle.

Copper, zinc and manganeseStrategic supplementation of three

important minerals leads to higherconception rates in artificially inseminated(AIed) beef cows when compared withanimals that did not receive mineralsupplementation.

An excellent example of this type ofresearch was a two-year study reported inthe Journal of Animal Science and conductedby a team from Colorado State Universityled by Jason Ahola, beef Extension specialistat the University of Idaho. It confirmed whatwas long-suspected by animal nutritionists— that trace minerals copper (Cu), zinc(Zn) and manganese (Mn) played animportant part in reproduction.

It also showed, in the second year of thestudy, that AIed beef cows that werestrategically supplemented with NationalResearch Council (NRC)-recommendedlevels of copper, zinc and manganese duringcritical reproductive periods had measurablyhigher pregnancy rates than those that weredenied these three trace minerals during anextended period of time. This wasparticularly true when insemination wasadministered based on an observed estrus.

“Strategic supplementation is feedingcows minerals around the time ofphysiological need,” Ahola says, adding thatthis critical period in beef cows is just beforecalving through rebreeding. “We would startsupplementing in January and end it in lateJune.”

Minerals— Three trace minerals and one macromineral

hold particular relevance to seedstock producers who

want to maximize their reproductive potential.

by Ed Haagn

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@“Strategic supplementation is feeding cows mineralsaround the time of physiological need,” Jason Ahola,University of Idaho, says, adding that this critical periodin beef cows is just before calving through rebreeding.

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November 2007 ■ ANGUSJournal ■ 147

The studyAs Ahola explains, the study involved the

same animals over a two-year period. Onehundred and seventy-eight crossbred beefcows participated in the first year of thestudy. A remaining 148 completed the lastyear.

Cows were stratified by expected calvingdate, age, body weight, body condition score(BCS) and liver mineral status and assignedto one of three groups. A control groupreceived no copper, zinc or manganesesupplement during the entire 24 months ofthe study. A second group received 50%organic and 50% inorganic copper, zinc andmanganese. A third group received thosethree minerals in a 100% inorganic form.

All supplemented animals received theirminerals through free-choice feeders atrecommended NRC concentrations.Strategic supplementation periods lasted 192days the first year and 216 days the second.

While in Year 1 the pregnancy rates to AIin control cows and supplemented cows werethe same, there was a substantially differentoutcome in Year 2. Ahola notes that onalmost all levels, the groups that were fed thetrace minerals with their diet had measurablyhigher pregnancy rates when compared withtheir control group counterparts.

“In that second year the cows who hadnot received the three supplementalminerals for over a year had a harder timebreeding back to that synchronized AI,” hesays, adding that the pregnancy rates to AI inboth supplemented groups were at least 20percentage points higher than the controlgroup.

Other factorsZoBell, who works with seedstock

producers on a regular basis, says that it isn’tjust the individuals who fail to provide anytrace mineral supplements to their cowswho could be facing mineral-relatedreproductive problems. Cattle can bereceiving some trace minerals but notenough to support their systems during thatcritical period from late pregnancy throughconception.

“You are asking them to produce a calf, toproduce milk and then to rebreed,” ZoBellsays. “Everything has got to be in sync, alltheir requirements have to be met, orsomething is going to slip.”

He notes that there is a fine line betweenfeeding the appropriate levels of mineralsand shorting those animals of the necessarynutrients. ZoBell adds that under-supplemented animals rarely show any overtsign of a mineral deficiency.

“You can walk out into a herd and if theyare energy-deficient their condition score islower,” he says, noting the visibility of the

deficiency. “With minerals you can’t do that.”ZoBell points out that ranchers who

think they are feeding their cows adequatelevels of minerals may actually be failing todo so. “Every animal is an individual, andthere is no guarantee that all cows are goingto consume what they require,” he says.

Not all cows are equalThis became evident to researchers

conducting a supplement intake study atMontana State University. When feeding atotal protein, energy and mineral package,they quickly discovered that supplementallotment among the cattle in the study wasfar from equitable, with the average dry-matter (DM) supplement intake being 33%lower for 3- and 4-year-old cows comparedto 8- and 9-year-olds.

It was determined from observations thatolder, larger animals held a dominantposition in the herd hierarchy and weresuccessful in monopolizing the self-feeders.Only by segregating the cows in the herdinto separate age groups were they successfulin changing the dynamics responsible for theinequitable division of supplements.

Outside of modifying the hierarchy,another issue to emerge from the Montanastudy was the role that competition at thefeeder played in the distribution ofsupplements. Contradicting intuitivethinking, the research team discovered that acertain amount of competition couldactually increase the likelihood of moreanimals receiving supplements. While toomuch competition prevented smaller

CONTINUED ON PAGE 148

Table 1: Least squares means for initial body weight, body condition score,age and liver mineral status of multiparous cows

Treatments

Item Control ORGa INGb

No. of cows 59 60 59Age, years 5.83 6.17 5.71Body weight, kg 619.4 616.1 615.3Body weight, lb. 1,366 1,358 1,356BCSc 5.91 5.97 5.97Initial liver mineral status:

Cu, mg/kg of DM 55.1 42.8 66.5Zn, mg/kg of DM 99.7 98.2 99.2Mn, mg/kg of DM 7.2 6.7 7.2

aORG = 50% organic and 50% inorganic Cu, Zn and Mn.bING = 100% inorganic CuSO4, ZnSO4 and MnSO4.

BCS: 1 = emaciated; 9 = obese (Richards et al., 1986).

Table 2: Ingredient composition and laboratory analysis of three trace mineraltreatments

Trace mineral treatments

Item Control ORGa INGb

Ca2PO4, % 52.0 52.0 52.0NaCl, % 21.5 21.5 21.5Dried distillers’ grain, % 15.6 15.6 15.6MgO (52%), % 4.9 4.9 4.9Soybean oil, % 4.0 4.0 4.0Se (0.16%), % 1.9 1.9 1.9Anise-fenugreek dry, % 0.11 0.11 0.11EDDIc (79.6%), % 0.009 0.009 0.009Chemical analyses:

Ca, % 10.7 10.7 10.7P, % 11.4 11.4 11.4Cu, mg/kg of DM 6.2 1,038.2 1,087.2Zn, mg/kg of DM 17.1 3,173.1 3,241.0Mn, mg/kg of DM 15.2 2,921.3 2,895.3

aORG = 50% organic and 50% inorganic Cu, Zn and Mn.bING = 100% inorganic CuSO4, ZnSO4 and MnSO4.

EDDI = ethylenediamine dihydroiodide.

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animals from feeding, too little competitionencouraged animals to fight rather thanfeed. It was determined that the ideal goalwas to size the feeder space so that itencouraged a continual rotation of animalsaccessing the supplements.

In some circumstances, the researchersfound the best way to make sure all animalsreceived their necessary supplementationwas to change how they were fed. Theynoted that cows responded differently toeach system used. For example whensupplements were hand-fed, there was lessvariation in intake between cows than therewas on self-fed systems.

More is betterThe Montana researchers also

determined from their study that increasingthe target amount of supplements from 2pounds (lb.) per cow to 5 lb. per cow perday contributed to the likelihood that morecows would consume supplements and thevariability between high consumers and lowconsumers would be narrowed.

This doesn’t necessarily mean that theoverall cost of supplementation would haveto increase. Feeding frequency can bereduced to compensate for the change.

In their final recommendations, theMontana researchers noted that one of themost practical and cost-effective ways toensure that beef cows will consume mineralsupplements as adults is to condition themto consume them as calves.

For heifers and young adult cows that arenot already conditioned to consumingsupplements, the researchers recommendthey be confined to an enclosed area witheasy access to supplements for a few daysbefore being released onto the range.

Nutritionist input valuableModifying the feeding environment,

increasing access and conditioning cowsfrom an early age to consume supplementsare effective tools in helping improve thechances that all cows receive their neededsupplement levels, but ZoBell is quick tonote that there are some environmental

conditions that can jeopardize any free-choice supplement feeding strategy.

“If you are in a location with highsodium levels in the water or it isparticularly alkaline and you put mineralsout, it is hard to get cows to eat them,” hesays. “Free choice may not be the answer inthat case.”

ZoBell says one of the best ways aproducer can ensure each of his cows isconsuming the minerals she needs tosupport her reproductive system is to spendsome time with a qualified nutritionist whocan evaluate the operation’ssupplementation program.

From his own experience interactingwith livestock producers, ZoBell says he isalways surprised at what they can overlookif they are working without professionalinput. He cites, as an example, how aseemingly conscientious producerinadvertently under-supplements hisanimals by feeding all his cows the samelevel of supplements regardless of size.

“You put a 1,600-pound cow against a1,200-pound cow; her requirements arehigher,” he says. “To get her to recycle and doeverything she is supposed to do, it is goingto take more groceries, including theminerals.”

Phosphorous also importantZoBell adds that one mineral that is likely

to be affected by this discrepancy isphosphorous. “It is one of those minerals thatis involved in everything from metabolism toreproduction,” he says. “Phosphorous is amacromineral, so it is needed in largerquantities than the trace minerals.”

Studies that date back to the King Ranchof Texas in the 1930s have shown that aphosphorous deficiency will have a negativeeffect both on conception and calf survival.

Because levels of this mineral are usuallyhigh in grains and low in forage, cheap cornwas, until recently, an excellent source ofphosphorous for seedstock cattle.

While those who are now feedingdistillers’ grains (DGs) — also high inphosphorous — may not need to worryabout meeting their animals’ phosphorousrequirements, those on strictly forage-baseddiets may be facing a phosphorousdeficiency and the reproductive problemsassociated with that deficiency.

“The bottom line is find out therequirements for your herd and then, ifdeficient, feed minerals to compensate forthat deficiency,” ZoBell says.

Minerals — A ’s Hidden Ally CONTINUED FROM PAGE 147

Table 3: Reproductive performance of cows supplemented with different tracemineral treatmentsa

TreatmentsItem Control ORGa INGc

Estrous cyclicityd 26% (11/43)i 28% (13/46) 23% (11/47)Estrus observed within 72 83% (80/96) 77% (78/101) 77% (79/103)

hours of PGF2∝ administrationPregnancy rate to AI (Year 1)e 65% (34/52) 67% (36/54) 52% (29/56)Pregnancy rate to AI (Year 2)e 34% (15/44) 57% (26/46) 58% (25/43)Pregnancy rate of AI if 58% (46/80) 77% (59/77) 65% (49/75)

observed in estrusf

Pregnancy rate of AI if 19% (3/16) 13% (3/23) 21% (5/24)mass-inseminatedg

Overall pregnancy rate 89% (85/96) 93% (94/101) 95% (98/103)after 60-day seasonh

aValues reported are percentages, with ratios in parentheses.bORG = 50% organic and 50% inorganic Cu, Zn and Mn.cING = 100% inorganic CuSO4, ZnSO4 and MnSO4.dPercentage of estrous cyclicity at the beginning of the breeding season was evaluated in Year 2 only via thecollection of two blood samples at 10-day intervals. Cows were identified as “cycling” if at least one bloodsample had a serum progesterone concentration greater than 1.0 ng/mL, indicating the presence of afunctional corpus luteum (CL).eThere was a year × treatment interaction (P<0.02) for pregnancy to AI, so data could not be pooled acrossyears. For each year, the value includes all cows in the study because all cows were inseminated once (eitherbased on an observation of estrus with 72 hours after PGF2∝ administration or via mass-insemination at 72hours after PGF2∝ administration.fValues reported include only cows observed in estrus within 72 hours of PGF2∝ administration andinseminated based solely on this observation of behavioral estrus.gValues reported include only cows never observed in estrus and subsequently mass-inseminated at 72hours of PGF2∝ administration.hOverall 60-day pregnancy rate includes data from both years 1 and 2.iNumber of animals observed per number of animals evaluated.

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