Genetics

The Cuban Brown rabbit breed. Characterization of reproductive performance in western Cuba

0000-0002-2601-895XYoleisy García Hernández^{1  *}  , 0000-0001-8632-7036Raquel E. Ponce de León Sentí¹  , 0000-0002-8478-4433Yusleiby Rodríguez Calvo¹  , 0000-0001-9155-1040D. García Quiñonez¹ 

¹Instituto de Ciencia Animal, Apartado Postal 24, San José de las Lajas. Mayabeque, Cuba

Abstract

To characterize the reproductive performance of the Cuban Brown Creole rabbit breed, 7488 mating, 5,876 born litters, 5,601 live litters and 3,567 weaned litters were used between 2014 and 2018. The traits fertility, total and live born, viability at birth and at weaning, number of weaned, litter weigh and individual at weaning were studied. Statistical analysis was performed with the SAS statistical package. The statistic general mean, coefficient of variation and standard deviation were determined. The influence of the trimester (4 classes) and the year (5 levels) was analyzed with a mixed generalized linear model, whose random effect was the breeder in each mating/ kindling. Pearson correlations were also calculated between the studied traits. It was shown that the reproductive performance of this breed was affected by the trimester (P <0.05) and the year (P <0.0001). The 75% of the characters showed better performance, when the mating and kindling occurred in the first trimester with respect to the third. The effect of the year showed the influence on the conditions of each year, with maximum expression in 2014. The trait live born was the most stable in time, an advantageous performance for the prolificacy of this breed. High correlations (+0.80) were found between total and live born, and between the weaned number and the litter weight. The reproductive performance of this breed is conditioned by environmental factors, so by improving its management, its productivity can be increased and a sustainable use of this zoogenetic resource can be made.

Key words: rabbits; local breed; reproduction; environmental effects

The characterization and monitoring of zoogenetic resources is one of the strategic priorities for their conservation and use. This is because genetic resources for feeding and agriculture (GRFA) are essential to maintain and improve food production, as well as being an essential tool in adapting to the effects of climate change (^{Scherf and Pilling 2015}). Due to the availability of a wide variety of breeds with different adaptation characteristics, the locally adapted ones, which are among the most threatened, can be used to obtain more productive animals (^{Bélanger and Pilling 2019}).

In Cuba, the Cuban brown rabbits breed is considered a creole breed, which has an in situ conservation strategy, which is based, fundamentally, on its use in family rearing systems and genetic reserve preserves, as is the case with most of local rabbit breeds (^{Oficina Cubana de los Recursos Zoogenéticos2014}). However, about this breed there are few reports of its reproductive performance, reported only for the eastern part of the country by ^{Valliant (2012)}. When considering what was stated by ^{Abdel-Kafy et al. (2018)}, the characterization of this zoogenetic resource is a priority for the identification and improvement of its management, as well as to facilitate its conservation, especially when the current populations of western Cuba are the result of the repopulating process of genetic centers after the last scourge of the viral rabbit hemorrhagic disease (VRHD), which considerably reduced their numbers (^{Dihigo and Ponce de León 2006}).

The reproductive traits are the most important economic characteristics in the development of any rabbit breed and in its improvement program for intensive meat production, so they are essential in the profitability of this breeding. Therefore, the objective of this study was to characterize the reproductive performance of the local Cuban Brown breed in a genetic unit from the western Cuba.

Materials and Methods

To characterize the reproductive performance of the Cuban Brown breed, information was taken from 7488 mating, 5876 born litters, 5601 litters born alive and 3567 weaned litters, produced in the rabbit genetic unit from Mayabeque province, in western Cuba, from 2014 to 2018. The sheds or buildings are made of masonry, 12 m wide by 50 m long, and gabled fiber cement roofs.

Herd management. The animals intake commercial feed as meal (17-18% of crude protein, 10 -10.8 MJ of digestible energy and 6 -10% of crude fiber), which was mixed with wheat bran at the time of being supplied, obtaining a bulky food, feasible to scratch, which did not meet the animal requirements. This supplied food showed 70% of the requirement, according to the category. In addition, forage from medium to low quality, primarily king grass (Cenchrus purpureum), was offered ad libitum. Water and feed were daily offered in terracotta pots. The breeders complied with the phenotypic characteristics of the breed, described by ^{Pons et al. (2013)}.

The mating was natural during the early hours of the morning, once the heat status of the breeder was verified by observing the color and turgor of the vulva, following the rotational mating scheme between family lines within the same breed. The verification of gestation was performed by palpation, at 14-15 d post-mating. At 28 d of proven gestation, wooden nests were placed in the cages of the breeders, until 15 d postpartum. At killings, live animals (DA) and dead animals were counted, whose sum represented the total born (TB). Litters were not regrouped at birth so as not to affect the genealogy of animals. Weaning occurred at 35 d of age of the young rabbits, the number of weaned females and males were counted, the sum of which resulted in the weaned number per kindling (WN) and the litters were weighed LW35. The next mating were carried out from eleven days postpartum, which corresponds to a semi-intensive system.

From the controlled variables, others were calculated, such as fertility (FERT), all or nothing character (FERT = 0 when mating was not effective and FERT = 1 when the breeder became pregnant and gave birth), viability at born (VIABB = DA/TB*100) and at weaning (VIABW = WN/DA*100). With the litters weight (LW35) the individual weight at 35 d (INDW35) was determined using the formula INDW35 = (LW35/WN).

Statistical analysis. The trimester and year factors were determined to characterize the reproductive performance of this Creole breed on all the traits to be studied (FERT, TB, LB, VIABB, WN, VIABW, LW35 and INDW35). The statistical package SAS (^{Statistical Analysis System}) version 9.3 (2013) was used for this. Using the PROC MEANS, the statistics were determined: general mean, coefficient of variation (CV) and standard deviation (SD), to know the performance of these characters.

A mixed generalized linear model was applied to all the traits under study with the help of the PROC GLIMMIX and repeated measures, which considered the four trimesters (January-March, April-June, July-September and October- December) and the five years (2014, 2015, 2016, 2017 and 2018) as sources of variation of fixed effects. For the FERT the trimester and year of mating were considered, while for the rest, the trimester and year of kindling. In addition, the random effect of the breeder was considered, with repeated records in each reproductive event for fertility and number of kindling for the other traits, since they were females from different kindling. The variance-covariance structure was toeplitz. Once the distribution of the data was determined using the proc severity, the binomial distribution was applied, for the FERT, VIABB and VIABW traits, while for the other characters the gamma distribution and the log link function were used. In all cases, Tukey's multiple comparison test of means, modified by Kramer (^{Kramer 1956}), was used to determine the differences between means.

To find the phenotypic correlations (Pearson correlations) between the reproductive traits TB, LB, VIABB, WN, VIABW, LW35 and INDW35, the database with information from the weaned litters (3,567 observations) and the PROC CORR, also from the SAS was used.

Results and Discussion

The descriptive statistics of the performance of the reproductive traits of the studied population are showed in table 1. The average fertility recorded for this breed in the West exceeds by ten percentage units the values reported for this same breed in eastern Cuba (^{Valliant 2012}) and that of the California, Chinchilla, New Zealand, Semigigante and Caoba pure breeds in different studies. (^{Ponce de León et al. 1999}, ²⁰⁰², ^2003b and ^{García et al. 2020}). However, these breeds have advantages over the Cuban Brown for the TB, LB, VIABB and WN traits, although these means had similar values with respect to those reported by ^{Valliant (2012)} for this same breed in the eastern region.

Table 1 Descriptive statistics of the reproductive performance of the local Cuban Brown breed 

Traits	Number	General mean	Standard deviation	Coefficient of variation %
FERT, %	7488	81.53	38.81	47.60
TB, number	5876	5.42	1.58	29.15
LB, number		4.95	1.89	38.32
VIABB, %		90.04	24.58	27.30
WN, number	5601	2.38	2.20	92.21
VIABW, %		45.91	39.22	85.44
LW35, g	3567	2025	895	44
INDW35, g		552	73	13

Viability to weaning (VIABW) was lower than 50%. This result may have had an impact on the simultaneous gestation and lactation, as a consequence of the reproductive rhythm used (semi-intensive), and that the animals were given a food that did not fulfill their requirements. According to ^{Szendrö et al. (2019)}, under these conditions, the food must fulfill the requirements, necessarily, to avoid competition between the development of the new litter and the milk production for the lactating young rabbits. One way to avoid this would be to increase the energy levels in the breeder's diet to guarantee the obtaining of a new litter, without the loss of the other (^{Pascual et al. 2013}), or to make modifications to the reproductive rhythm in the case of large litters (over 6 young rabbits) and underweight females, with mating 25-30 d postpartum and weaning between 40 and 45 d.

The litter weight (LW35) and individual weight (INDW35) at weaning is also similar to that reported for the population studied by ^{Valliant (2012)} in eastern Cuba, where temperatures are higher between one and three degrees Celsius (^{INSMET 2018}) .The Caoba, one of the breeds that is considered to have participated in the origin of the Cuban Brown genotype, had a general mean for the litter weight of 2,232 g, but similar individual weight (554 g) according to a study by ^{Ponce de León et al. (1999)}. For the California, Chinchilla and New Zealand breeds, ^{García (2019)} registered upper means of litter weights with 2,699 g and 635 g for each young rabbit.

The superiority of other breeds evaluated in Cuba with respect to the Cuban Brown may be given by the improvement processes to which their populations have been subjected at different times, since the beginning of rabbit breeding in the country (^{Ponce de León 2010}). Meanwhile, the Cuban Brown genotype is incorporated into the work of genetic improvement as a pure breed and inbreeding control in western conditions, in 2014. In this regard, ^{Kumaresan et al. (2011)} pointed out that the sustained selection of a breed for particular environments is essential to obtain satisfactory productive results. However, when analyzing the average performance of the reproductive traits of this breed in the five years of study, a certain advantage is recognized with the use of this genotype for fertility and pre-weaning growth traits (LW35 and INDW35).

The reproductive performance of this creole breed is influenced by the environmental effects of the trimester (P <0.05) and year of kindling (P <0.0001), in correspondence with that described for the species by ^{Lebas et al. (1996)}. This result agrees with the effects identified by a group of authors (^{Ponce de León et al. 2003a}, ^b, ^{Vásquez et al. 2007}, ^{Valliant 2012} and ^{García et al. 2020}) for different rabbit breeds, as causes of variation that affect the zootechnical performance of reproductive traits. These effects are a consequence of the reproductive and nutritional management imposed on the animals, and also of the differences in environmental conditions between the kindling seasons (^{Apori et al. 2014}).

The effect of the trimester in which kindling occurred on the studied traits is shown in table 2. Of the eight indicators studied, 75% (FERT, TB, LB, WN, LW35 and INDW35) reached the highest values, when the mating and kindling occurred in the first trimester of the year (January-March), when temperatures are lower and favor the reproductive process (^{Ogunjimi et al. 2008} and ^{Askar and Ismail 2012}). In accordance with that stated by ^{Asemota et al. (2017)}, under the climatic conditions of the tropics the reproductive potential in rabbits is limited. This is accentuated during the summer months (July-September), due to the fact that the animals are exposed to average temperatures higher than those of their thermal comfort zone (18-25ºC), which is why physiological mechanisms are developed that cause this deterioration (^{Marai et al. 2007} and ^{Cruz-Bacab et al. 2018}).

Table 2 Effect of the trimester on the reproductive traits of the local Cuban Brown breed 

Traits	January-March		April-June		July-September		October-December
	Mean	±SE	Mean	±SE	Mean	±SE	Mean	±SE
FERT, %	88.79^a	0.09	84.32^b	0.16	83.04^c	0.11	88.28^ab	0.08
TB, number	5.51^a	0.04	5.46^ab	0.05	5.36^b	0.04	5.40^ab	0.05
LB, number	5.30^a	0.05	5.15^ab	0.05	5.12^b	0.04	5.19^ab	0.04
VIABB, %	91.39^ab	0.03	90.14^b	0.04	91.70^a	0.03	92.42^a	0.04
WN, number	4.25^a	0.07	3.42^c	0.08	3.62^c	0.06	3.96^b	0.06
VIABW, %	48.10^b	0.07	23.44^d	0.06	32.85^c	0.06	63.71^a	0.07
LW35, g	2485^a	42	1934^c	44	1985^c	36	2184^b	31
INDW35, g	590^a	3	576^b	4	558^c	3	562^c	2

^{a, b, c, d} Means with different superscripts in the same raw differ at P < 0.05 (^{Kramer 1956}).

The survival percentage of young rabbits, at kindling (VIABB) and at weaning, (VIABW) was favored during the last trimester of the year (October-December) with respect to the whole of the months of April, May and June, when these traits showed the lowest values. These months coincided with high levels of rainfalls in the province, more than 100 mm (^{INSMET 2018}), and it may be that the young rabbits were not sufficiently protected. This is one of the causes of high mortality, identified by ^{Lebas et al. (1996)}, together with the insufficient feeding of lactating rabbits. In addition, the high temperatures of the summer months cause a reduction in food intake by the breeders. According to ^{Amroun et al. (2018)}, when this happens, the availability of milk for young rabbit decreases during the lactation period and their survival is reduced.

The effect of the year on the reproductive traits studied (table 3) reflects the influence that the specific conditions of each year have on the performance of these characters, mainly due to the great variations in the diet. ^{Ponce de León et al. (2003a)} and ^{Ortega et al. (2014)} also reported that the environmental effects of the season (season- kindling year) were important for reproductive traits, with a highly variable performance of the rabbits through the years.

Table 3 Effect of the kindling year on the reproductive traits of the local Cuban Brown breed 

Trait	2014		2015		2016		2017		2018
	Mean	±SE	Mean	±SE	Media	±SE	Mean	±SE	Mean	±SE
FERT, %	90.89^a	0.07	87.68^b	0.09	85.24^bc	0.12	82.46^c	0.12	86.68^bc	0.18
TB, number	5.61^a	0.06	5.59^a	0.05	5.23^c	0.05	5.32^b	0.04	5.42^ab	0.05
LB, number	5.35^a	0.06	5.23^a	0.05	5.07^b	0.05	5.09^b	0.05	5.20^a	0.05
VIABB, %	90.22^bc	0.05	89.92^c	0.04	93.69^a	0.04	91.39^b	0.04	91.51^b	0.04
WN, number	4.57^a	0.10	3.56^c	0.05	3.33^d	0.06	3.78^bc	0.08	3.95^b	0.06
VIABW, %	11.63^e	0.05	59.85^b	0.07	45.14^c	0.08	27.88^d	0.06	73.28^a	0.06
LW35, g	2960^a	129	1965^c	30	1790^d	32	2137^bc	45	2008^b	29
INDW35, g	652^a	8	561^b	2	560^b	3	568^b	3	524^c	2

^{a, b, c, d, e} Means with different superscript in the same raw differ at P < 0.05 (^{Kramer 1956})

In general, in 2014 the best performance of the studied traits was found, perhaps due to the progressive deterioration of the quality of the food supplied to the animals in the following years, not only due to the lack of raw materials, but also due to their contamination. Inadequate reproductive management, health problems that affected the mass of breeders and the interruption of genetic improvement work between 2016 and 2017 may also have had an impact on these results. This corresponds to what was showed by ^{Lukefahr et al. (1983)}, who affirm that the year is a complex effect, because it involves climatic factors, such as management and production technologies. These results indicate the need to stabilize and improve the nutritional and management environment to increase the productivity of this local or creole breed based on its in situ conservation and achieve productive increases, as showed by ^{Abdel-Kafy et al. (2018)}.

Despite the variations found in the reproductive performance of this breed, it was stated that the trait live born was the most stable in the five years analyzed, indicative of an advantageous performance for the prolificacy of this breed. This performance is similar to that reported by ^{García et al. (2020)} for California breed, also in western Cuba.

The Pearson correlations between the reproductive traits of the Cuban Brown are shown in table 4. As expected, high, positive and significant correlations were found, with values higher than 0.80 between live born and total born, and between the weaned number and the litter weight at weaning.

Table. 4 Pearson's correlations between the reproductive traits of the local Cuban Brown breed 

	TB, number	LB, number	VIABB, %	WN, number	VIABW, %	LW35, g	INDW35, g
TB, number		0.85*	0.01	0.49*	-0.14*	0.46*	-0-11*
LB, number			0.51*	0.60*	-0.14*	0.56*	-0.14*
VIABB, %				0.60*	-0.06*	0.32*	-0.09*
WN, number					0.66*	0.94*	-0.21*
VIABW, %						0.62*	-0.13*
LW35, g							0.12*
INDW35, g

*p < 0.0001

Also positive, but moderate dependencies (0.50 to 0.80), were found among live born with the weaned number and litter weight, as well as between the weaned number and viability at weaning, and between the latter and litter weight at weaning. However, the individual weight at weaning has little link, in the opposite, with the other indicators analyzed, less with the LW35, where the correlation is positive.

The low and negative correlations found in this study between TB, LB and WN with the survival of the young rabbits until weaning (VIABW) presuppose that at higher litter size, the viability is lower. This is due that the food requirements to support large litters were not satisfied, causing this genotype not to achieve high productions until weaning. However, ^{Ponce de León et al. (2003a)} found mean correlations (0.38 to 0.44) between total and live born with respect to pre-weaning mortality in imported breeds, fed with better quality pelleted feed.

In Nigeria, in a study on the reproductive performance of four rabbits breeds under humid tropic conditions, ^{Fadare and Fatoba (2018)} reported Pearson correlations very similar to those recorded here between total born and weaned number, and between the weaned number and the litter weight at weaning, where as one increases the other increases.

In this study, the advantage that the use of this Creole genotype can have for fertility and pre-weaning growth traits was evidenced, as well as the influence of season effects (trimester and kindling) on the reproductive performance of this breed. The knowledge of these causes of variation is necessary to make fitted in their management, fundamentally in relation to reproduction and feeding, to optimize the performance of traits related to weaning (WN, VIABW and LW35). This, together with the restart of genetic improvement study through selection, will allow increasing the productivity of this breed, conserving it properly and making a more sustainable use of this animal genetic resource in western Cuba.

Acknowledgments

Thanks to the technician Marta Mora Hernández, from Instituto de Ciencia Animal, for her collaboration in preparing the databases used in this study.

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Received: March 02, 2021; Accepted: May 05, 2021

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Conflict of interest: The authors declare that there are no conflicts of interests among them

Author´s contribution: Yoleisy García Hernández: Original idea, design of the experiment, data analysis, manuscript writing. Raquel E. Ponce de León Sentí: Design of the experiment, manuscript writing. Yusleiby Rodríguez Calvo: Statistical analysis, manuscript writing. D. García Quiñonez: Conducting the experiment, data base.