Introduction
Reproductive efficiency is a major determinant of economic viability in cow-calfproduction systems. In its simplest form, reproductive outcome pertains to theability of a cow to calve and wean a calf every year. Previous studies havedetermined that the calving rates in Mexico (number of females calving relative tothe total number of cows exposed to the bull) are between 40 and 50%.1 In a nationwide study commissionedby the Ministry of Agriculture2 thepregnancy rate of the national herd was 32%, which implies an annual calving rate of55%. Thus, the biologic potential of grazing cattle and the related reproductiveoutcome of cow-calf systems in Mexico are currently below their possibilities.
Grazing cattle farms are extensive production systems that occupy a vast and valuablestretch of the Mexican territory, affecting the quality and preservation ofecosystems. This impact can be further determined by the environmentalsustainability of the production system itself. Previous studies have shown thatchanges in reproductive efficiency of the herd can directly affect land and wateruse characteristics, as well as greenhouse emissions. In fact, researchers foundthat reducing the calving window, twinning, and implementing management practicessuch as early weaning decreased the environmental impact by 3.2%, 9.2% and 8.3%respectively.3
Establishing the reproductive efficiency of a herd by calving rate only issimplistic, as this parameter is also affected by numerous factors including age atfirst parturition, pregnancy rate, cow and bull fertility, etc. However,reproductive traits generally have a low genetic heritability, thus grantingsignificance to management environmental factors for the successful production ofweaned calves. This study aimed to investigate the frequency of management practicesin cow-calf systems in Mexico that may influence the reproductive efficiency of theherd. These include breeding strategies, use of reproductive technologies, pregnancydiagnosis, criteria for first mating heifers, feed supplementation, age at weaning,diagnosis and prevention of reproductive diseases and breeding soundness examinationof the bull. Data were obtained through structured interviews administered directlyto the managers of more than 3000 cow-calf production units across the country.
Materials and methods
Management practices and use of technology in grazing cattle production units inMexico were characterized by a structured questionnaire that gathered descriptiveinformation related to farm organization, broad management of the herd, occurrenceof infrastructure, feeding practices, health and well being, environmentalmanagement practices, reproductive management, handling of calves, dual-purposesystems, and a section devoted to specialized dairy production in pasture. Thisstudy deals with the reproductive management of the herd.
The questionnaire was adapted from the one used by the United States Department ofAgriculture (USDA) to characterize beef-calf management practices in the UnitedStates of America,4 consideringadjustments and suggestions offered by experienced academics, technicians andfarmers from different regions of Mexico.
The methods and questionnaire are described in Gonzalez-Padilla etal.5 Briefly, thesample size was calculated with a 95% confidence level, with a probability (p) of50% and an estimated error (d) of 5%.
The calculated number of questionnaires to be administered was 3158.5 A total of 3311 questionnaires werecompleted, of which 31 were discarded due to answer discrepancies. Finally, onlyfarms with beef or dual-purpose herds were included for this paper, eliminatingmixed herds with both purposes and specialized dairy herds in pasture. The finaldatabase was conformed of 3280 entries (Figure1).
Figure 1Distribution of surveyed beef and dual-purpose cattle operations,according to established agro-ecological regions.
Statistical analyses
Each possible option within a question was considered as a binary variable. Thefrequency of each management practice was analyzed by REML. The results areshown as least square means and standard error of the difference (sed).Differences are declared at p < 0.05.
Fixed variables were considered as follows:
Herd size: defined as small (up to 35 cows), medium (36 to 100 cows)and large (over 100 cows).
Region: the country was arbitrarily divided in five regions accordingto their similarity in agro-ecological characteristics andgeographical proximity, namely: North (Baja California, BajaCalifornia Sur, Chihuahua, Coahuila, Durango, Nuevo León, Sonora andZacatecas); Center (Aguascalientes, Estado de México, Guanajuato,Hidalgo, Puebla, Querétaro, San Luis Potosí and Tlaxcala); Pacific(Chiapas, Colima, Guerrero, Jalisco, Michoacán, Morelos, Nayarit,Oaxaca and Sinaloa); Gulf (Tabasco, Tamaulipas and Veracruz), andPeninsula (Campeche, Quintana Roo and Yucatán).
Climate: classified as arid-semiarid, temperate, dry tropics andhumid tropics, according to Garcia.7
Poverty levels were defined following municipal categories set by theNational Population Council8 as very low, low, medium, high and veryhigh.
Land-tenure type was declared by the producer as communal land, ejido(government owned land allocated to usufructuary farmers) or privateproperty.
Results and discussion
Over 90% of producers in Mexico expose their cows to bulls year-round, whilst only6.3% use seasonal breeding. Although scarce, this latter practice is more common inthe northern region of the country (Table 1).Likewise, large operations use seasonal breeding more often (10.76%) than small(4.27%) or medium-size farms (6.02%) (Table1). Even if domestic cattle can reproduce throughout the year, studies showthat there is a seasonal calving pattern in cow-calf operations, which relates to anenhanced fertility in cows that overlaps the months with greater pastureavailability. Indeed, a calving record assessment of a zebu herd in the wet tropicsin Mexico shows that females calve preferably during the winter and spring months,despite being exposed to the bull year-round.9 Moreover, in septentrional Europe, feral cattle herds
Table 1Percentage of cow-calf operations* that execute either year-round,seasonal or split-season breeding strategies, considering populationmean, region of the country where farms are located and herd size.
Annual breeding strategy | sed | |||
---|---|---|---|---|
Year-round | Seasonal | Split-season | ||
Population mean | 93.10 | 6.31 | 0.49 | 0.54 |
Region | 1.21 | |||
North | 83.30 | 15.60 | 0.88 | |
Pacific | 96.15 | 3.63 | 0.22 | |
Center | 92.43 | 6.90 | 0.67 | |
Gulf | 92.34 | 6.77 | 0.74 | |
Peninsula | 99.49 | 0.25 | 0.00 | |
Herd size | 0.94 | |||
Small | 95.35 | 4.27 | 0.31 | |
Medium | 93.54 | 6.02 | 0.44 | |
Large | 88.03 | 10.76 | 0.91 |
* The sum of the proportions in a given row can differ from 100%,since presented values correspond to minimum quadratic means and/orbecause more than one answer was possible.
sed: standard error of the difference.
have a defined calving season when no supplementary feed is provided.10 Therefore, considering thenatural seasonality of cattle may prove advantageous for producers.
Methods to synchronize estrus are rarely used in cow-calf systems in Mexico (9.1%),even if more frequent in large and privately-owned farms (Table 2). The questionnaire did not enquire for the specificmethods of synchronization used. Nonetheless, regardless of the protocol,wide-ranging advantages of estrous synchronization programs in a cowherd includeadvancing mating and shortening the calving interval, as well as a more effectiveuse of timed artificial insemination, which can overcome the shortcomings of heatdetection and use of bulls.11,12
Table 2Percentage of cow-calf operations* that use estrus synchronizationprotocols, considering population mean, herd size and land tenuretype.
Use of synchronization protocols | ||
---|---|---|
sed | ||
Population mean | 9.11 | 0.76 |
Herd size | 1.35 | |
Small | 7.00 | |
Medium | 7.67 | |
Large | 15.33 | |
Land tenure | 1.58 | |
Ejido | 6.59 | |
Communal | 4.53 | |
Private | 12.04 |
* The sum of the proportions in a given row can differ from 100%,since presented values correspond to minimum quadratic means and/orbecause more than one answer was possible.
sed: standard error of the difference.
Most grazing cattle production units use natural breeding (97.4%), and only 4.6% ofthe farms use artificial insemination (AI). These frequencies do not seem to beimpacted by the productive purpose of the farm (beef vs.dual-purpose), or by the age of females (cows vs. heifers).However, use of AI is more common in large and in privately owned operations (Table 3). The limited use of AI found forcow-calf operations in Mexico is a deterrent for the advancement of the geneticmakeup of the national herd, since selection pressure is lower when using naturalservice (bulls). Concurring with the low frequencies found for practices such assynchronization and AI, estrus detection is used in merely 20% of the productionunits. Again, similar frequencies were found for this management practice for beefand dual-purpose cattle, as well as for heifers and cows.
Table 3Percentage of cow-calf operations* that use different mating methods,considering population mean, herd size and land tenure type.
Mating method | sed | |||
---|---|---|---|---|
Artificial insemination | Cow taken to the bull | Natural service at pasture | ||
Population mean | 4.57 | 1.25 | 97.40 | 0.43 |
Herd size | 0.76 | |||
Small | 2.36 | 1.07 | 97.03 | |
Medium | 4.25 | 1.42 | 97.93 | |
Large | 9.38 | 1.36 | 97.43 | |
Land tenure | 0.88 | |||
Ejido | 1.87 | 1.33 | 97.78 | |
Communal | 1.92 | 0.32 | 98.40 | |
Private | 7.23 | 1.38 | 96.90 |
* The sum of the proportions in a given row can differ from 100%,since presented values correspond to minimum quadratic means and/orbecause more than one answer was possible.
sed: standard error of the difference.
As for the criteria that producers use to determine when to mate their heifers forthe first-time, the predominant factor was age (Figure2). Interestingly, even when the customary technical recommendation isthat a heifer should reach 65% of its mature body weight before being bred, bodysize and weight were only used as decisive reasons in 35% of operations (Figure 2). Moreover, it has been previous
Figure 2Criteria that producers use to determine when to mate their heifersfor the first-time (values shown are percentage of the surveyedoperations. sed = 1.07).
ly established that heifers should be first mated between 14 and 16 months of age inintensive pasture systems, hence calving for the first time at two years ofage.13 Nonetheless, mostMexican producers mate their heifers for the first time after 2 years of age (73%),indicating that sexual maturity and puberty may be generally occurring late. Similarobservations for this and other countries have been reported elsewhere.14
Forage availability and nutrient deficiencies are additional factors that may impactcalving seasonality and delay puberty of heifers.15 Rainfall variability across the differentagro-ecological regions of Mexico, with precipitation being more common during thesummer and autumn months, and a drought period of greater or lesser extent duringwinter and spring, is an undisputed element impacting animal access to naturallygrowing grass. Thus, cattle supplementation is essential to avoid excessive bodycondition loss and decreased productive performance. A 63.4% of producers in Mexicogive energy or protein supplements to their cattle, mostly in spring, coincidingwith the draught period (Figure 3a). Inaddition, this type of supplementation is more frequent in dual-purpose than in beefcattle operations (75.5% and 57.1%, respectively; sed = 1.91). Moreover, feedsupplements are rarely given during the autumn months, when pasture is most abundantdue to the rainy season (2.6%). All year-round supplementation was reported by closeto 28% of operation units (Figure 3a). Inaddition, this management practice is more common in temperate, arid and semiaridclimates than in humid or dry tropical conditions (Figure 3b).
Figure3. Use of energy or protein feed supplementation considering (A)season or (B) climate (values show percentage of the surveyed operationsthat provide supplements, season sed = 1.3; climate sed = 2.85).
When supplements are provided, they are given to all the animals of the herd (68%).Strategic supplementation based on individual physiological status is not frequentlyused (Table 4). However, when implemented,beef cattle farmers favor lactating animals over pregnant cows (Table 4). It is well known that strategicsupplementation has better results when used to bolster body condition score atcalving (ideally a BCS: 3 or above in a 1 to 5 scale should be reached). Indeed,cows calving in a better BCS have shorter postpartum intervals.16 Thus, supplementation must have enough energydense content to meet maintenance requirements of
Table 4Percentage of cow-calf operations* that provide energy or proteinfeed supplements to the cattle at different physiological stages,considering population mean and productive purpose of theoperation.
Group of animals | sed | |||||||
---|---|---|---|---|---|---|---|---|
Suckling cows | Breeding cows | Finishing cattle | Pregnant cows | Milking cows | Backyarding cattle | All | ||
Population mean | 14.62 | 2.27 | 2.03 | 5.61 | 15.04 | 2.39 | 68.20 | 0.96 |
Productive purpose | 1.35 | |||||||
Beef | 10.45 | 2.51 | 2.61 | 5.63 | 6.53 | 2.51 | 77.69 | |
Dual purpose | 20.70 | 1.91 | 1.17 | 5.58 | 27.46 | 2.20 | 54.33 |
* The sum of the proportions in a given row can differ from 100%,since presented values correspond to minimum quadratic means and/orbecause more than one answer was possible.
sed: standard error of the difference.
late pregnant cows and allow for an increase in BCS.15 For dual-purpose cows, supplementation is also aimedto improving milk production, hence this practice was followed thrice as often inthis type of operations, when compared to beef cattle production systems (Table 4).
Concentrate is undoubtedly the most frequently used supplement by farmers (37.3%),followed by chopped forages and hay (33.3% and 28.6%, respectively), whilst silageis only used by 18.7% of producers (Table 5).Preference of concentrate use over other supplement choices is probably due both toits ready availability and its high energy and protein content. Concentratesupplementation is also more frequent in dual-purpose farms than in beef cattleoperations (Table 5), since it can benoticeably linked to an immediate increase in milk production.
Table 5Percentage of cow-calf operations* that use the different types ofnutritional supplements, considering population mean and productivepurpose of the operation
Type of supplement 350. | sed | ||||||
---|---|---|---|---|---|---|---|
Concentrate | Chopped forrage | Hay | Silage | Nutritional blocks | Other | ||
Population mean | 37.30 | 33.30 | 28.60 | 18.70 | 17.00 | 14.60 | 1.45 |
Productive purpose | 2.10 | ||||||
Beef | 32.30 | 35.80 | 31.30 | 18.50 | 18.10 | 16.30 | |
Dual purpose | 44.60 | 29.60 | 24.60 | 19.10 | 15.50 | 12.10 |
* The sum of the proportions in a given row can differ from 100%,since presented values correspond to minimum quadratic means and/orbecause more than one answer was possible.
sed: standard error of the difference.
Grass-fed cattle also require supplementation of mineral nutrients not sufficientlyfound in pasture. An adequate mineral mix should be specifically customized toprovide the micronutrients that are deficient in the forage grown at the farm. Thisstudy did not assess the adequacy of the mineral mixtures given to the animals.However, most farmers do provide mineral preparations to their cattle (79.1%), withthe use of common salt persisting (15%), and 9.2% of the producers do not supplementminerals at all (sed = 0.93). Mineral addition to feed, either common salt or mixedmineral formulations, are given throughout the year (86.9 ± 0.7) to all animals ofthe farm (91.5 ± 0.52).
To attain a successful cattle breeding program, a further critical managementpractice is pregnancy diagnosis. Surprisingly, only 30.8% of operations declared tocheck cows for pregnancies and 54.4% do not diagnose pregnancy at all. Also, 15% ofthe producers declare the use of non-return to estrus as an indicator of gestation(Table 6). When implemented, the mostcommon method for pregnancy diagnosis is transrectal palpation, whilst ultrasoundexamination is used in less than half a percentual point of the surveyed farms.Pregnancy diagnosis is more frequent in large operations (58.7%), when compared tomedium or small-sized operations (< 45%; Table6). Methods to detect pregnancy are mostly performed by a professional(74%; veterinarian or animal scientist), followed by the farm manager (26%).Non-pregnant cows are normally kept in the farm and mated again, with only 23% ofoperations declaring absence of pregnancy as a criterion to discard animals. Themost common reasons for culling cows in herds are old age (64%), infertilityproblems (26.3%), and the need to generate cash flow (13.3%).
Table 6Percentage of cow-calf operations* that diagnose pregnancy,considering the method used and the effect of herd size.
Method used to presume or diagnose pregnancy 409. 410. | sed | |||
---|---|---|---|---|
Transrectal palpation | Non-return to estrus | Ultrasonography | ||
Population mean | 30.35 | 15.61 | 0.42 | 1.00 |
Herd size | 1.74 | |||
Small | 23.95 | 16.07 | 0.08 | |
Medium | 28.07 | 17.43 | 0.44 | |
Large | 46.27 | 12.18 | 1.07 |
* The sum of the proportions in a given row can differ from 100%,since presented values correspond to minimum quadratic means and/orbecause more than one answer was possible.
sed: standard error of the difference.
Pregnancy diagnosis is perhaps the most decisive technology to monitor reproductiveefficiency of any breeding program. However, results of this study show that thispractice is extremely disregarded in cow-calf operations in Mexico. Similarly, asurvey conducted by the Department of Agriculture of the United States revealed lowimplementation of pregnancy diagnosis methods among farmers, which increased withsize of the herd (10.8% in herds < 50 cows up to 58% in herds > 200 cows; USDAAPHIS).17 Interestingly, alarge-scale reproductive study including more than 347 thousand cows examined bytransrectal palpation in 7994 Mexican farms, showed that 32% of the animals werepregnant and that 40% of the non-pregnant cows were cycling.2 These findings further expose an important area ofopportunity to improve reproductive efficiency of the national herd by theimplementation of pregnancy diagnosis in production units.
Adequate calf weaning strategies can also improve reproductive performance of thebreeder herd. This study shows that 85% of cow-calf operations in Mexico wean theircalves between 6 months and one year of age. The most common approach for weaning isabrupt separation (69.4%), while nose plates to prevent calf suckling are used by17.4% of producers, and restricted suckling by 13.1% (Figure 4). Reports show that separation stress is reduced when noseplates, rings or flaps are used, since calves remain in the company of theirdams.18 Also, the negativeeffects on the immune response and weight loss of the calf that generally ensue anabrupt weaning practice are minimized.19 Further, the use of nose flaps helps to maintain a higherBCS in the cows, which improves their reproductive efficiency.20,21 Restricted suckling on the other hand has been shownto advance the resumption of postpartum ovarian cyclicity and increase pregnancyrates.21 Nonetheless, thislatter practice is not favored by the farmers as they believe that it is extremelystressful for young animals and requires special accommodations, as well asadditional provisions to impede cows and calves from seeking to reunite during thisperiod.
Figure 4Calf weaning strategies used in cow-calf operations in Mexico (valuesshow the percentage of the surveyed operations that use each method; sed= 0.9).
Prevention of abortive diseases is paramount for the productivity of the cowcalfproduction system, the main tool being vaccination. Nonetheless, prevalence ofvaccination was remarkably low in the surveyed farms, even for mandatory report andcompulsory immunization diseases such as brucellosis (16%). Vaccines against otherreproductive diseases, namely BVD, IBR, PI3 or leptospirosis was even lower (<18%). Conversely, extended results of this study show that over 70% of the farmersdo vaccinate their animals against potentially life-threatening diseases.22 Thus, it appears that producersneglect to appreciate welfare and economic losses that can be prompted by chronicreproductive diseases.
Breeding soundness examination of the bull plays an important role in herdreproduction. However, only 40.8% of the surveyed farms in this study have had theirsires declared as fit at some point for entering a breeding program. Moreover,breeding soundness examination is performed mainly at the time of purchasing thebull (33.9%), and rarely prior to breeding or at an annual basis (Table 7). Previous studies in Chihuahua1 and Costa Rica23 have shown that when examined, 15% and 23% of thebulls respectively were not fit to reproduce. Similarly, 25% of the sires were ruledas unfit for breeding in a US report.24 Furthermore, results of this study show that specificdiagnosis of venereal diseases of the bull is executed in merely 20% of farms. Whenperformed, reproductive disease diagnoses are mainly directed to brucellosis(19.7%), since surveillance is compulsory as part of the government campaign fordisease control in livestock species. However, the presence of other venerealdiseases, such as trichomoniasis, vibriosis or IBR/BVD/IBR is rarely established(< 2%). These results can be striking when considering that the preferred methodfor breeding the females in cow-calf systems in Mexico is by direct service, whichconflicts with the very little attention that is given into ensuring the breedingsoundness of bulls. Finally, the main criteria for bull replacement are to avoidinbreeding (68.4%) and advanced age (26.8%). Other reasons are seldom considered.
Conclusions and implications
The results of this study showcase a low adoption of reproductive managementpractices by cow-calf operations in Mexico. Advancement of these practices, as wellas implementation and promotion of associated technologies, denotes an area ofopportunity to improve the reproductive efficiency of the national herd.