Suppressing Immature House and Stable Flies in Outdoor Calf Hutches with Sand, Gravel, and Sawdust Bedding

E. T. SCHMIDTMANN Livestock Insects Laboratory

Agricultural Research Service, USDA Beltsville Agricultural Research Center

Beltsville, MD 20705

ABSTRACT

Sand, gravel, sawdust, and pine shav- ings were used as bedding in outdoor calf hutches and compared with straw relative to the density of immature (mag- got) house flies, Musca domestics, and stable flies, Stomoxys calcitrans. In 6-wk field trials, average densities of house and stable fly maggots in concrete mix sand ranged from only .3 to 1.6 and 0 to .1 maggots& respectively; pea size gravel bedding also strongly suppressed densities from <.1 to .3 and <.I to .1 maggots& respectively. These densities represent reductions of 76 to >99% rela- tive to straw bedding, but both sand and gravel compacted and became soiled with calf feces, which resulted in unac- ceptable bedding sanitation and foul odors. Densities of house and stable fly maggots in pine shavings did not differ from those in straw bedding. Neverthe- less, in sawdust bedding, maggot density was limited to averages of 1.4 to 8.3 house and 9.8 to 11.8 stable fly maggots/ L; this represented reductions of 45 to 91% relative to straw. In a follow-up trial, house and stable fly maggot densi- ties in sawdust averaged 11.3 and 43.9 maggot& respectively, reductions of 77 and 46%. These findings suggest that bedding calf hutches with sawdust dur- ing warm weather can be useful as an ecologically sound approach to control- ling muscoid fly populations on dairy farms. (Key words: flies, bedding, calf hutches)

Received January 30, 1991 Accepted May 30, 1991.

INTRODUCTION

Dahy farming creates numerous habitats that support the growth and development of immature (maggot) house flies, Musca domes- tics, and stable flies, Stomoxys calcitrans. Ac- cumulations of manure, spilled grain, and si- lage (7), as well as the management practice of bedding dairy calves with straw, create an ideal environment for immature house and sta- ble flies (6, l l , 16). As further evidence of this relationship, averages of as many as 50 to 70 house fly and 12 to 20 stable fly maggots& were found in the bedding of outdoor calf hutches on dairy farms in Maryland (13); these densities represent an estimated potential for producing 25,000 to 40,OOO adult flies per hutch per summer. Adult muscoid flies com- promise dairy sanitation, bother animals and farm workers (4), and represent a potential for fly dispersal into adjacent urban homes where they are a public health concern.

The specific microhabitat requirements for muscoid maggots are unknown, but materials rich in OM and with a moisture content of 60 to 90% are favored (15, 17). Furthennore, microbial activity has been shown to be impor- tant, if not essential, to house fly maggot growth (5, 8). Because substrates lacking these factors can be expected to limit maggot de- velopment and because suppressing maggot growth is fundamental to controlling adult muscoid populations (l), the use of bedding materials that are unsuitable for muscoid mag- gots represents a potential method for limiting adult muscoid fly abundance on dairy farms. Oak sawdust, wood chips, ground corncobs, and sand bedding have been shown to suppress muscoid maggot density in dairy calf pens and hutches (9, 14). This paper evaluates sand, gravel, pine shavings, and sawdust for effect on muscoid maggot density when used as bed- ding in outdoor calf hutches.

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SUPPRESSING FLIES

MATERIALS AND METHODS

Experlmental Deslgn

Five 6-wk trials, each involving 15 newborn Holstein calves housed individually in calf hutch units, were conducted from mid-June to mid-September during the summers of 1988, 1989, and 1990. Hutch Units consisted of 1.4- x 1.9-m molded fiberglass shelters (Fiber- dome Inc., Lake Mills, wr) and adjoining ex- ternal areas of 1.4 x 1.9 m enclosed by welded-mesh wire. Hutches were set side by side at 3-m intervals in parallel rows on either packed and leveled soil or a crushed rock- fabric filter system. The fiiter system consisted of a base pad of crushed rock (5 to 10 cm in diameter and 20 to 40 cm in depth) and a sheet of polypropylene hydraulic fabric (Polyfilter GB, Carthage Mills, Cincinnati, OH). The fab- ric mesh was 21 to 26% open area, equivalent to a US standard sieve number 40 (.42 mm). Hutch units were placed individually on 3- x 6-m sheets of fabric separate to the hutch and bedding material from underlying rock and to facilitate drainage. Test bedding materials (treatments) were allocated randomly among filter system and packed soil sites in each trial; each material was replicated in at least five hutches. Test bedding materials were 1) straw (unchopped), one bale per hutch; 2) concrete mix sand, a mixture of particles of approxi- mately .5 to 2.0 mm in diameter; 3) pea size gravel, a washed mixture of particles that ranged from approximately 2 to 5 mm in di- ameter; 4) millrun sawdust (mixed hard- woods); and 5) pine shavings (grade number 3). Newborn calves were placed in hutch units at the start of each trial and held in the same unit for a 6-wk period. Bedding was not re- moved during this interval, a practice consis- tent with calf-hutch management on commer- cial dairy farms; fresh bedding was added as needed to maintain reasonable sanitation.

Treatment Evaluatlon

Bedding substrate was sampled weekly for muscoid maggots by taking 1-L samples of bedding from the inside center and outer en- closure center areas of each hutch; these sites consistently are inhabited by house and stable fly maggots (13). Samples of straw, pine shav- ings, and sawdust were transferred to Berlese-

IN CALF HUTCHES 3957

Tulgren units for separation of maggots. Bed- ding samples were turned over and mixed to promote drying and extraction of maggots. Sand and gravel samples were examined by spreading them in a white enamel pan (20 x 40 cm). The substrate was scanned under illumi- nation, disturbed, and scanned repeatedly over a 5-min period. All maggots collected by either method were preserved and temporarily stored in 5% formalin before being identified and counted.

The numbers of second-instar and third- instar house and stable fly maggots recovered from each sample were either all identified by spiracular plate morphology (samples contain- ing no more than 25 specimens) or all counted and the size and species composition of the sample estimated on the basis of 25 randomly selected and identified specimens. Sample values were subjected to a log (n + 1) transfor- mation to normalize the variance. An ANOVA was computed (12) to examine the effects of treatment, area of hutch, sample date (week), and interactions. Transformed least squares means were tested for significance by pairwise comparisons (12); significance was preset at the .05 level.

RESULTS

The density of house fly maggots in straw bedding on packed soil and filter system hutch sites was low in the 1988 and 1989 trials, averaging 6.6 and 15.0 maggotsb for straw and 6.0 and 3.0 maggotsb for straw and filter (Table 1). Stable fly maggots were abundant in straw on both packed soil and filter system sites, averaging 64.6 and 52.4 maggotsb for straw and 66.7 and 54.9 maggotsb for straw and filter (Table 1). In contrast, house fly maggot density in concrete mix sand on packed soil sites averaged only 1.6 maggots,L (Table 1). a significant reduction of 76% rela- tive to straw. No stable fly maggots were detected in the 60 samples of concrete mix sand Densities of house and stable fly mag- gots were low in concrete mix sand over the fabric filter and averaged -3 and <.l maggots/ L, respectively; these means represent signifi- cant reductions of 95 and >99% relative to straw (Table 1). Pea size gravel bedding on packed soil supported little maggot growth; house and stable fly maggot densities averaged

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TABLE 1. Density of immature house 0 and stable flies (SF) in materials uscd as experimental bedding in outdoor calf hutches.

Average rmmber of Perctntage of maggots per sample reduction'

HF SP HF SP - Bedding type

?? SE X SE 1988 straw 6.6 1.9 64.6 8.7 . . . . . . Straw plus filter 6.0 .1 66.7 9.5 9 . . . Sand 1.6. .7 0, 1.5 76 100 sand plus filter .3* .3 <.l* 1.5 95 >99 Gravel .3* .3 .l* 1.5 95 >99 Gravel plus filter .I* .3 <.1* 1.5 >98 >99

Straw plus filter 3.0 1.7 54.9 12.2 80 . . . pine shavings 6.4 2.1 59.8 12.4 57 . . . pine shavings plus fdler 15.4 5.3 34.1 6.7 . . . 35

Sawdust plus filter 8.3 3.0 11.8* 3.8 45 77

1989 straw 15.0 5.4 52.4 8.4 . . . . . .

Sawdust 1.4 1.1 9.8* 3.2 91 81

1990 Straw 49.3 14.5 81.0 10.5 . . . . . . Sawdust 11.3 14.5 43.4* 10.5 77 46

'Average number of maggots per sample (treatment) x lOO/average number of maggots per sample (control). *Mean differs from that in spdw bedding (P = 05).

.3 and .1 maggotsb, respectively. This represents significant reductions of >98 and 99% relative to straw. Extremely low house and stable fly maggot densities were observed in gravel bedding over the filter system, .1 and <.1 maggots& respectively; this further illus- trates that sand and gravel are unsuitable sub- strates for muscoid maggot growth. House fly maggot density in pine shavings

on packed soil and filter system sites did not differ from straw and averaged 6.4 and 15.4 maggots/L, respectively (Table 1). Stable fly maggot density in pine shavings on packed soil and filter system sites did not differ from straw and averaged 59.8 and 34.1 maggot& respec- tively. In sawdust bedding on packed soil, house and stable fly maggot densities averaged 1.4 and 9.8 maggotsb in the 1989 trials (Table

spectively; only stable fly maggot density was signifkantly less than in straw bedding. In 1990, densities of house and stable fly mag- gots in straw averaged 49.3 and 81.0 maggots/ L, respectively, and in sawdust they averaged 11.3 and 43.4 maggotsb, respectively. These means represent reductions of 77 and 46%. but

l), Which are reductions Of 91 and 81%, re-

Journal of Dairy Science Vol. 74. No. 11, 1991

only stable fly maggot density was signifi- cantly less than in straw bedding.

In 1988, interactions of bedding type x week and filter system x week were significant for house fly data, and bedding x week was significant for stable fly data. There were no significant interactions for either house or sta- ble fly data in the 1989 trials or for house fly data in the 1990 trials. Week, hutch x week, and location x week interactions were signifi- cant for stable fly data in the 1990 study.

DISCUSSION

The consistent disparity in numbers of house and stable fly maggots in sand and gravel versus straw bedding illustrates that the former materials strongly suppressed maggot density and, accordingly, are unsuitable as sub- strates for muscoid maggot growth. With saw- dust bedding, average house fly maggot den- sity during the 1989 trials was lower than in a previous study (14) and later trials (1990), i.e., averages in 1989 of approximately 5 to 8 versus 30 to 50 maggot& in the 1990 trials (Table 1). Nevertheless, house fly maggot den- sity in sawdust on packed soil hutch sites

SUPPRESSING FLIES IN CALF HUTCHES 3959

averaged apparent reductions relative to straw of 91% in 1989 and 77% in the 1990 trials. These values were not statistically significant reductions, which presumably reflects strong variation in house fly maggot density among weekly samples attributable to the contagious distribution of maggots in afeas of sawdust mixed with manure. The density of stable fly maggots, which are seldom found in fresh manure, was significantly lower in sawdust than straw bedding the first 2 yr of the study with average reductions of 81 and 46%. There- fore, it is reasonable to conclude that sawdust bedding in calf hutches is a marginal environ- ment for house and stable fly maggots. This interpretation is consistent with the reduced house fly maggot density in oak sawdust re- ported by MacCreary and Haenlein (9) as well as the low density of both house and stable fly maggots in calf hutches bedded with coarse sawdust on a commercial dairy (13). Calf hutch bedding is only one of several organic substrates common to dairy farms that support the development of immature muscoid flies (11,16), but the use of sawdust bedding in calf hutches during warm weather may prove u s e ful to dairy producers as an ecologically sound approach to managing muscoid fly popda- tions.

In addition to the direct effect of bedding type on maggot density, the variable week and interactions of bedding type x week were sig- nificant in several t r i a l s . This condition pre- sumably reflects sporadic rainfall, cumulative soiling of bedding with manure, and the short generation time of muscoid flies at summer temperatures. Because the F values associated with these interactions were small relative to the F values for bedding type, there is reason to think that bedding type was the principal factor that regulated maggot density.

The basis for suppression of maggot density in sand and gravel bedding presumably lies in the unabsorbent, largely inorganic nature of these materials, a condition that may inhibit maggot growth physically or nutritionally or may limit oviposition by female flies. House fly maggots require a complex diet of organic compounds (3) coupled with microbial activity (5), and female house flies generally oviposit only on moist organic materials. MacCreary and Haenlein (9) attributed lesser densities of

house fly maggots in oak sawdust than in peanut hulls to a lower pH and less fermenta- tion. Furthermore, the decomposition of saw- dust, which consists largely of lignified fiber, results in a high carbon to nitrogen ratio that inhibits microbial activity (2). It can be hy- pc&esized that the chemical and physical na- ture of sawdust limits microbial activity and substrate decomposition, thus differing from manure and soiled straw; this may explain why it is an unfavorable environment for growth of house and stable fly maggots. In laboratory tests, moist sawdust does not support house fly maggot growth unless it is mixed with at least equal amounts (by weight) of fresh bovine manure (unpublished data). The presence of house and stable fly maggots in sawdust bed- ding in calf hutches presumably reflects the mixing of sawdust with accumulations of ma- nure and spilled feed.

Despite their efficacy in suppressing the density of house and stable fly maggots, sand and gravel bedding, readily compacted and soiled with calf urine and feces, becomes fouled and unsanitary after several weeks of calf occupancy. This condition, which also was noted previously with river bank sand used as bedding in calf hutches (14), was intensified by rainfall. The fabric filter system was used to enhance drainage of bedding and delay bed- ding compaction. Nevertheless, sand and gravel bedding on both packed soil and the filter system not only compacted and soiled, but both materials also generated foul (anaero- bic) odors; therefore, they are not acceptable as bedding for calf hutches. Straw bedding also becomes compacted and fouled with calf feces, particularly when wetted by rainfall, and the resulting bedding “pack” promotes muscoid maggot growth (10). The addition of fresh straw over soiled bedding to maintain calf comfort and sanitation, a common manage- ment practice, can be expected to enhance muscoid maggot growth by increasing the moisture-holding capacity and fermentation potential of the bedding pack An appreciation of these relationships and a recognition that bedding materials other than straw can be used in calf hutches to limit muscoid maggot d e velopment can benefit dairy producers con- cerned about controlling muscoid fly popula- tions.

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ACKNOWLEDGMENTS

The author thanks Jennifer Koch and Gloria Marselas for invaluable assistance in conduct- ing field and laboratory aspects of this study.

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